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Cognitive Neuropsychology

ISSN: 0264-3294 (Print) 1464-0627 (Online) Journal homepage: http://www.tandfonline.com/loi/pcgn20

Pure alexia and covert reading: Evidence from Stroop tasks

Thomas J. McKeeff & Marlene Behrmann

To cite this article: Thomas J. McKeeff & Marlene Behrmann (2004) Pure alexia and covert reading: Evidence from Stroop tasks, Cognitive Neuropsychology, 21:2-4, 443-458

To link to this article: http://dx.doi.org/10.1080/02643290342000429

Published online: 28 Nov 2010.

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Download by: [St Lawrence University] Date: 20 May 2016, At: 12:01 COGNITIVE NEUROPSYCHOLOGY, 2004,21(2/3/4) 443-458

PUREALEXIA AND COVERT READING: EVIDENCEFROM STROOPTASKS

ThomasJ. McKeeff and Marlene Behrrnann Carnegie Mellon University, Pittsburgh, PA, USA

Patients with pure alexia (also referred to as letter-by-letter readers) show a marked word-length effect when naming visually presented words, evidenced by a monotonic increase in response time (or decrease in accuracy) as a function of the number of letters in the string. Interestingly, despite the difficulty in overtly reporting the identity of some words, many patients exhibit fast and above-chance access to lexical and/or semantic information for the same words. To explore the extent of this covert reading, we examined the degree of interference afforded by the inconsistent (word identity and colour label do not match) versus neutral condition in a Stroop task in a pure alexic patient, EL. EL shows evidence of covert reading on a semantic categorisation task and a lexical decision task. She also demonstrates covert reading by exhibiting Stroop interference of the same magnitude as a matched control subject, when naming the colour of the ink in which a word is printed. When the word shares some but not all letters with the colour name (BLOW instead of BLUE), neither subject shows interference. In contrast with the control subject, EL does not show Stroop interference when various orthographic changes (degraded visual input, cursive font) or phonological or semantic changes are made to the word. These findings indicate that although some implicit processing of words may be possible, this processing is rather rudimentary. Not surprising, this implicit activation may be insufficient to support overt word identification. We explain these findings in the context of a single, integrated account of pure alexia.

INTRODUCTION fibers in the splenium of the corpus callosum or forceps major (Black & Behrmann, 1994; Damasio Pure alexia is a neuropsychological disorder in & Damasio, 1983). The lesion site is also compat- which premorbidly literate adults exhibit severe ible with recent functional imaging data, which reading impairments in the absence of other point to these regions as implicated in reading (for obvious language deficits (for a recent review, see recent paper, see L. Cohen, Lehericy, Chochon, & & Lemer, Rivaud, & Dehaene, 2002; Hasson, Levy, Downloaded by [St Lawrence University] at 12:01 20 May 2016 Behrmann, Plaut, Nelson, 1998b; Coslett Saffran, 2001). The disorder is a consequence of Behrmann, Hendler, & Malach, 2002). Patients brain damage typically located in the left occipital with this disorder are also termed letter-by-letter lobe but can also result from damage to callosal (LBL) readers because they appear to process

Correspondence should be addressed to Thomas J. McKeeff, Department of Psychology, Princeton University, Princeton, NJ 08544, USA (Email: [email protected]). This paper is submitted as a special tribute to Dr Eleanor Saffran whose contribution to the field of Cognitive Neuropsychology was immeasurable. She was a true inspiration to us. This work was supported by funding from the National Institute of Mental Health to MB (MH47566 and MH54246). We thank Matt Lambon Ralph, Rachel Mycroft, and Marie Montant for their useful suggestions.

02004 Psychology Press Ltd 443 http://www.tandf.co.uk/journals/pp02643294.html DO1:lO. 1080/02643290342000429 MCKEEFF AND BEHRMANN

letters sequentially when attempting to read a identify five- and six-letter words at an exposure word. This LBL reading behaviour may manifest duration of 2 s. However, ML was able to make a in the overt articulation of individual letters but, lexical decision to similar five- and six-letter words more often, is evident in measures of the accuracy and nonwords at above-chance levels. This ability or reaction time of their word processing (for was also mediated by the frequency of the words, in example, in naming or lexical decision tasks). that ML was more accurate at classifying high- as Whereas normal readers require minimal, if any, opposed to low-frequency words. ML was also able extra time to read a word as the length increases to make semantic classifications (e.g., does the (up until approximately nine letters; Frederiksen, word represent a living or nonliving thing?) of 1976; Weekes, 1997), suggesting parallel process- briefly presented words at levels much higher than ing of the letters, LBL readers show a linear would be expected by guessing, even though he still increase in their reading time and eye movements could not explicitly identify the target word. (Behrmann et al., 2001) as a function of the Another surprising finding that is apparent in number of letters in the string. This monotonic several LBL readers is the presence of the word relationship between word length and naming superiority effect. The word superiority effect, latency is assumed to reflect the sequential pro- defined as the increase in accuracy and decrease in cessing of the individual letters in the string response time to detect an individual letter within (Warrington & Shallice, 1980). a word as opposed to a nonword, is thought to arise from the activation of the entire letter string, with greater activation for words than for nonwords. The presence of the word superiority effect in LBL Covert processing in readers LBL readers is counterintuitive. If LBL reading is Despite the apparent failure to process letters in accomplished purely in a bottom-up sequential parallel with normal efficiency and the subsequent fashion through activating individual letters, there adoption of the serial processing of letters, some is no obvious reason that lexical status would exert patients with pure alexia demonstrate covert or any influence on performance. However, there are unconscious processing of words. Although they now many reports of individuals in whom a word may not be able to identify a word overtly, they superiority effect has been documented (Bub, appear to have available to them both lexical and Black, & Howell, 1989; Reuter-Lorenz & Brunn, semantic information about the word even when it 1990; for the same finding using a different is presented at exposure durations too brief to paradigm, see Behrmann & Shallice, 1995). support explicit identification. Additionally per- Although reports of covert processing in LBL plexing is that, when assessed in these covert are fairly common nowadays, many LBL readers processing conditions, the word length effect is do not show implicit reading, performing at often absent (Bub & Arguin, 1995; Coslett & Downloaded by [St Lawrence University] at 12:01 20 May 2016 chance levels on lexical and semantic decision tasks Saffran, 1989). (see Arguin et al., 1998, for discussion of this An early demonstration of this implicit reading point). It has been suggested that the absence of phenomenon comes from work by Landis, Redard, these covert effects occurs because the individual and Serrat (1980) in a description of a LBL reader attempts to read sequentially (even when who, when shown a word for 30 ms, could not instructed not to) and that this serial strategy identify it and sometimes denied even seeing the inhibits the output of the covert processing system. word. Yet, when instructed to match the presented According to Coslett and colleagues (Coslett & word to an object displayed amidst an array of Saffran, 1994; Coslett, Saffran, Greenbaum, & several objects, he was accurate a significant pro- Schwartz, 1993), there is a fundamental opposition portion of the time. Shallice and Saffran (1986), in between the strategies involved in covert word a more systematic study of covert word reading, processing and those for overt word recognition. described a patient ML who could not explicitly The implication is that covert processing is more

444 COGNITIVE NEUROPSYCHOLOGY, 2OO4,21(2/3/4) PURE ALEXIA AND COVERT READING

reliably revealed when the patient is not simultane- Covert processing and representational ously attempting to identify the stimulus explicitly. precision The use of a paradigm that does not engage explicit reading is therefore advantageous in uncovering Even if one can demonstrate the presence of covert covert word processing. One technique that has processing using this Stroop paradigm, an open proven fairly profitable in a number of recent question concerns the extent and precision of the studies is the use of a priming paradigm in which representations activated during implicit reading. the patient does not respond to the prime (and Some researchers have argued that the representa- hence supposedly does not engage in serial tions activated implicitly are well specified and processing) but responds to the probe (for example, precise whereas others have suggested that this is Arguin et al., 1998). However, given that the not the case. For example, recent studies using the probe is also a word and that the patient is engag- implicit priming paradigm have explored whether ing in some word processing, one might imagine words that differ from the target stimulus by a that the patient is attempting to read the prime single letter are activated when a word is presented too. To better understand the nature of covert (Bowers, Arguin, & Bub, 1996a; Bowers, Bub, & processing in LBL reading, the task we adopt in Arguin, 1996b). If so, this might suggest that a less the current paper does not require word reading in precise representation is activated. To evaluate the the conditions of interest and may be especially specificity of the representation, these studies use a useful for revealing implicit reading. priming paradigm in which subjects name a briefly The task we have adopted is a Stroop paradigm presented (100 ms) upper-case word. Prior to the and the particular condition of interest is the one in appearance of this target, a prime in lower case, is which subjects name the colour of the ink rather shown and then backward masked. Even though than read the word. In the original Stroop task the exposure duration of the target was brief, (Stroop, 1935), subjects performed both word and substantial reductions in RT (reaction time) were ink naming tasks in blocked fashion. In the word observed when the prime and target were the same naming task, participants read the word presented, compared with when they were different (even if while ignoring the ink colour of the words. In the the case was mixed, Arguin et al., 1998). However, ink naming task, participants named the stimulus if the prime differed from the probe by just a single ink colour, while ignoring the word in which it was letter in any position of the word, no priming was presented. Of particular interest is the comparison evident. Given the absence of priming by a near in naming the ink colour in two conditions: the orthographic neighbour, these studies conclude control condition, in which nonword stimuli are that the entire string must have been precisely and used (e.g., several Xs or rectangles) and the incon- covertly activated. gruent condition (for example, the word BLUE, A somewhat different result has been obtained

Downloaded by [St Lawrence University] at 12:01 20 May 2016 written in red ink). This comparison is especially in further studies by some of the same investiga- relevant because, under these conditions, subjects tors. Using the same masked priming task, Arguin do not name the word but only name the colour ink et al. (1998) have shown that, in contrast to normal and therefore do not explicitly engage word recog- readers, there is no facilitation in the performance nition processes. Any cost in latency observed in of their LBL patient, IH, if the prime is homo- the incongruent over control condition, when phonically related to the target. IH also does not subjects are required to name the ink colour, is show facilitation from increased orthographic taken as evidence for the automaticity of word neighbourhood size, again suggesting that covert reading (Kahneman & Henik, 1981; but see activation is not entirely normal. Besner, 2001). If LBL patients are able to activate Whether or not activation is rich and precisely any lexical or semantic information covertly, ink specified, however, has important theoretical sig- colour naming will be significantly slower in the nificance. As alluded to previously, at least one incongruent than in the control condition. account of covert processing in LBL readers, the

COGNITIVE NEUROPSYCHOLOGY, 2004,21(2/3/4) 445 MCKEEFF AND BEHWNN

"right hemisphere account," has argued that the hemisphere working in tandem with the intact covert reading arises from a different procedure right hemisphere (Behrmann et al., 1998b). from that used for LBL reading. Whereas the Because of the brain damage, full elaboration of former reflects parallel processing in the right the representation of the word is not possible and hemisphere, the latter depends on serial and any covert effects arise from the partial activation sequential processing generated by the damaged of the input that is derived under the brief exposure left hemisphere. Additionally, the left hemisphere conditions. is responsible for explicit word identification and In addition to using the Stroop paradigm to phonological processing, while the right hemi- explore covert processing, the further goal of this sphere supports covert word processing. Clearly, paper is to explore the precision of the activated most LBL readers encode the visual stimuli in the representation. To do so, we compared EL'S per- right hemisphere initially due to the right visual formance with that of a matched control subject in field defect, which is present in most, although not the control and incongruent conditions of the all, LBL readers. According to this view, the right Stroop ink naming task in a series of experiments hemisphere processing extends beyond perceptu- in which we manipulate the phonological, lexical, ally encoding the stimulus and may, in fact, be orthographic, and semantic status of the word in responsible for all implicit reading. The right hem- an attempt to document the range and extent of isphere activation is sufficient to give rise to the implicit reading. covert processing seen in these patients, but cannot mediate the output of the phonological form for overt production, hence the failure to explicitly GENERAL METHODS report the word. On this view, then, the represen- tation activated implicitly is detailed and rich but Participants the information is not transmitted to the left hem- Patient EL, previously diagnosed as a LBL reader, isphere for output (Coslett & Monsul, 1994; participated in this study. A detailed case report of Coslett & Saffran, 1994; Saffran & Coslett, 1998). EL (as well as scans of her lesion site) is available Note that, on this account, the sequential process- in previous publications (Behrmann, Nelson, & ing may interfere with the covert activation and Sekuler, 1998a; Montant & Behrmann, 2001). EL inhibit the ability to derive lexical and semantic is a 50-year-old, native English speaking, right- representations in the right hemisphere. handed female with 18 years of schooling. She was An alternative view argues against two separate admitted to the hospital in April 1996 for right processes, one for implicit and one for explicit arm weakness, blurred vision, and slurred speech reading, and claims that the covert reading arises caused by two embolic events. A CT scan per- from the residual function of the normal reading formed at the time of admission revealed a large

Downloaded by [St Lawrence University] at 12:01 20 May 2016 system. Because of the brain damage, a rather infarction in the territory of the left posterior coarse and imprecise representation might be cerebral artery involving the left peristriate infero- activated implicitly by the conjoint functioning of temporal visual association cortex, the postero- the right hemisphere and the residual left hemi- lateral temporal cortex, and the dorsal parietal sphere, and this activation may suffice for some cortex in the vicinity of the occipitoparietal cortex. tasks but not for others. The failure to report the EL does not exhibit any obvious visual agnosia word explicitly might then arise because naming although, in certain experimental conditions, her requires a more precise and refined representation ability to name pictures is affected by their of the input and this is not sufficiently specified. structural complexity (Behrmann et al., 1998a). According to this account, even when the patient EL does not display any writing or spelling diffi- is not engaged in serial word processing, word culties but, as expected, she fails to read easily what processing is mediated by a single unified system she herself has written on a previous occasion. that reflects the residual capabilities of the left Premorbidly, EL was an avid reader. Ironically and

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sadly, she was trained as a remedial specialist and Methods worked with children who had developmental Lexical decision. EL completed three blocks of a reading problems. lexical decision task, using the same set of words EL is able to identify single letters extremely used in the naming latency task described well, even under brief presentation. At the time of above. Each block consisted of randomly pre- this testing, we re-measured EL's word length sented three-, five-, and seven-letter words and effect by having her read aloud words of three, five, . ..,.--. nonwords. derived from the words with one or two and seven letters, presented to the left of a furation vowel changes, for a total of 150 trials in the cross on a computer screen for an unlimited experiment. A trial was initiated with a centrally exposure duration. EL made no errors in reading located futation cross, which remained on the but required an additional 403.7 ms per letter in .,...... a screen for 1000 ms. A word or non-word. dis- the word (calculated by setting string length played in Aria1 24pt font, then replaced the against RT in a regression analysis). Her mean RT furation cross in the same location on the screen, was 1490.81 ms, 2345.07 ms and 3103.70 ms for and was presented for 300 ms, an exposure three-, five-, and seven-letter words, respectively. duration far too brief for EL to identify the word This linear increase has rou~hlvremained the same ...... 4. 0 J (her naming latencies indicate that she requires for several years now (Behrmann, 1998a; Montant roughly 400 ms per letter). The stimulus was then & Behrmann, 2001) and puts her in the class of replaced by a mask of seven instances of the letter mild to moderate LBL readers (Behrmann et al., "X that appeared in the same position as the pre- 1998: Shallice. 1988). . .. -...... - --. .. . - vious stimuli. 1 his mask remained until res~onse. '1'0 compare EL'S performance with that of a I EL was instructed to determine whether the letter non-brain-damaged individual, we tested QK, string was a real word or a nonword and to respond who was also right-handed and was matched to with an appropriate button press. Accuracy and EL on age, gender, and education. RT were recorded.

Apparatus and materials Semantic classzj?cation. This procedure has been used repeatedly to establish whether LBL readers All experiments were conducted on a Macintosh can assign words to a semantic category despite the G3 PowerBook. Stimuli were presented on a 14.1 failure to read them explicitly (Behrmann & Shal- in (35.8 cm) colour monitor using PsyScope exper- lice, 1995; Patterson &Kay, 1982; Shallice & Saf- imental software version 1.2.1 0. D. Cohen, fran, 1986). This task consisted of 100 words, half MacWhinney, Flatt, & Provost, 1993). All voice of which are food items and half body parts, responses were obtained using a desktop computer divided equally into items of four, five or six letters microphone (Radioshack, Fort Worth, TX) and in length. Trials followed the same procedure and

Downloaded by [St Lawrence University] at 12:01 20 May 2016 voice onset time and key responses were obtained timing as the lexical decision task above. EL was using a Button Box (New Micros, Dallas, TX). instructed to determine whether the word referred Participants were seated approximately 50 cm from to a food item or body part and to respond with an the monitor. The experimenter noted the verbal appropriate button press. This task was repeated responses made by the participants. twice, 2 weeks apart.

EXPERIMENT 1 Results Before adopting the Stroop procedure, we first Lexical decision. EL performed significantly above document EL's ability to show covert word chance with 114 out of 150 trials correct (76%), processing using the more standard techniques of x2(1, N) = 150) = 20.7 ,p < .0001. Even under this lexical decision and binary semantic classification. brief duration, she showed an effect of word

COGNITIVE NEUROPSYCHOLOGY, 2004,21(2/3/4) 447 MCKEEFF AND BEHRMANN

length, with higher accuracy for three- compared colour matched the words presented (e.g., the to five- letter words, x2(1, N) = 100) = 8.41,~< word BLUE printed in blue ink). All words in the .003. She also showed an effect of lexicality, with control condition were printed in black ink. In the greater accuracy for nonwords than words, incongruent condition, the words displayed did x2(1, N)= 150) = 6.2,~< .012; however, this may not match the ink colour but were in one of the reflect a bias to respond "no" when she is uncertain other possible ink colours used (e.g., the word (d' = 1.58). BLUE, printed in yellow ink). In the ink naming task, participants were Semantic decision. EL attempted to read aloud 361 required to name the ink colour of the words that 200 words. She was incorrect on 26 of these, but all were presented on the screen. The stimuli used in of these were excluded from the analysis of interest. both the ink naming congruent and incongruent Of the remaining 164 words, she correctly conditions were the same set of stimuli as in the classified 101 (62%), a result suggesting that she congruent and incongruent word naming task. The performed significantly above chance, x2(1, N = control condition for ink naming consisted of a 164) = 8.8,~< .003, and has access to the semantic string of the letter "X (with the Xs printed in the information of words that she cannot overtly iden- appropriate colour), which varied in length to tify. These findings suggest that EL has some match the number of letters in each of the colour covert processing ability on these more standard words used. implicit tasks. The question is whether we will The design in this study was entirely within- observe interference in the Stroop colour naming subject, with the independent variables being task task. (word naming and ink naming) and congruency condition (congruent, control, and incongruent). This resulted in a total of six different conditions, EXPERIMENT 2 which were blocked. Each block was prefaced with the task instructions and was followed by 20 The goal of this next experiment is to examine randomised trials followed by a short break. Prior whether EL shows Stroop interference and, if so, to the experiment, participants were given two whether the interference is comparable in magni- blocks of 20 practice trials, one each of word and tude to that obtained in a normal reader. If this ink naming. The subjects were told to respond as were the case, it would suggest that the extent of quickly as possible without sacrificing accuracy. the implicit (automatic, in this case) representation RT was measured from the time the words were is not different from that activated by normal presented on the screen until a response was made. readers. The experimenter recorded word and ink naming errors. Participants completed the experiment and

Downloaded by [St Lawrence University] at 12:01 20 May 2016 then, after at least 2 weeks, repeated the entire Methods experiment (with the block order reversed) result- Words were printed in capital letters in Chicago ing in a total of 240 trials, 40 in each condition. 48 pt font. The list of words used in this experi- ment included the colour words blue, green, purple, red, and yellow. The ink colours chosen Results and discussion were the same as each of the colour words. In this Error trials, trials on which the microphone did first experiment, we collected data from the word not trigger at the correct time, and trials yielding and ink naming task. RT values greater than 4 SDs from each subject In the word naming task, participants were mean were all excluded from the analysis, resulting required to read aloud the printed word presented in a removal of 5% of the data for QK and 8.3% for centrally on the screen as quickly and as accurately EL. No subject made more than two naming errors as possible. In the congruent condition, the ink in any of the conditions, so accuracy performance

448 COGNITIVE NEUROPSYCHOLOGY, 2OO4,21(2/3/4) PURE ALEXIA AND COVERT READING

is not analysed. The data for each subject were latency in other reading tasks; however, this is entered into a 2 x 3 (Task x Condition) analysis of expected given the small set of words used in this variance, comparing the tasks of word naming and Stroop task. EL also showed a main effect of con- ink naming. All painvise comparisons were done gruency, F(2, 214) = 17.6,~< .0001, and the task using Tukey post hoc comparisons with an alpha by condition interaction was significant as well, level of .05. The results are shown in Figure 1. F(2, 214) = 7.1, p < .0001. Like QK, EL did not The mean RT for the task of word naming show any differences among the three word for the control subject, QK, (460.1 ms) was faster naming conditions (p > .05) but showed significant than the mean RT for ink naming (626.6 ms), interference in ink naming, with the RT for the F(1,222) = 210.8,~< .0001. A main effect of con- ink naming-incongruent condition (867.2 ms) gruency was also observed, F(2, 222) = 69.8, p < 194.5 ms slower than for ink naming-control .0001. Importantly, the task by condition interac- (672.8 ms) (p < .05). EL also did not show facilita- tion for QK was also significant, F(2,222) = 49.8, tion in the ink naming-congruent condition @ > p < .0001. QK did not show any differences bet- .05) (see Figure 1). While EL is slower than QK in ween conditions in the word naming task @ > .05). both tasks, F(1, 440) = 93.8,~< .0001, there is no She did, however, show the Stroop effect, with ink task by subject interaction nor a three-way inter- naming-control (542.8 ms) being faster than ink action with condition (p > .05). , naming-incongruent (804 ms), an increase of In sum, both subjects showed a similar pattern 261.2 ms @ < .05). In the ink naming task, QK did of data, with no effect in the word naming con- not show facilitation in the congruent condition dition as a hnction of congruency, but a large (p > .05) compared to the control condition. Over- Stroop effect as shown by an increase in RTs in the all, EL responded faster for word naming (599.2 ink naming-incongruent condition compared to ms) than ink naming (724.9 ms), F(1,214) = 43.4, the control condition. These results are similar to p < .0001. EL'S word naming in this task is faster those typically found in Stroop experiments (see compared to her response times for word naming Macleod, 1988). The findings indicate that the

T Downloaded by [St Lawrence University] at 12:01 20 May 2016

Congruent Control Incongruent Congruent Control lncongruent

Word naming

Ink naming

Figure 1. Response time in a colour Stroop task as afunction of task (word naming and ink naming;)and condition in EL and controlsubject QK.

COGNITIVE NEUROPSYCHOLOGY, 2004,21(2/3/4) 449 MCKEEFF AND BEHRMANN

Stroop paradigm is indeed effective in revealing names of the colours. The design in this study was the covert processing in a LBL reader and that EL entirely within-subjects, with the independent var- appears to activate representations of words iables being ink naming condition (standard words implicitly to the same extent as le control subject. and onset control words) and congruency condi- tion (congruent, control, and incongruent). Sub- jects completed three blocks of each of the ink EXPERIMENT 3 naming conditions with a long break between each block. Each of the three conditions was balanced Having demonstrated that EL s subject to inter- so that an equal number appeared in each block. ference from the incongruent word in the ink There were 36 trials in each condition, which naming task, suggesting covert processing of letter resulted in a total of 216 trials for each participant, strings, we now explore the nature and extent of with an equal distribution of both stimulus type this interference. This next experiment was and congruency condition. designed to replicate the results in Experiment 2. Each trial began with a centrally positioned fur- Additionally, this condition was intended to elim- ation cross that appeared for 500 ms. The coloured inate the possibility that the Stroop interference word stimuli then immediately replaced the cross seen in EL was merely a result of interference and remained on the screen until the participant caused by reading the first letter(s) and not the responded. Participants were told to name the entire word. To do this, we included an ink naming- colour of the stimuli verbally as quickly as possible onset control condition in which words were without sacrificing accuracy. RT was measured chosen to share the first letter(s) with colour words from the time the colour word stimuli was pre- (e.g., BLOW for BLUE and PURITY for sented on the screen until a voice response was PURPLE) (for similar control conditions, see made. The experimenter recorded ink naming Berti, Frassinetii, & Umilti, 1994; Patterson & errors and microphone errors. Kay, 1982). Results and discussion Methods Trials on which the microphone did not trigger at The onset control words used in this study were the correct time and trials with RT values greater chosen to match both the word length and also the than 4 SDs from each subject mean were excluded first or first few letters of the colour words. The from the analysis, resulting in a removal of 3.2% of onset control words chosen were BLOW for blue, the data for QK and 3.7% for EL. Naming errors GROUP for green, PURITY for purple, RAW occurred infrequently, so accuracy performance is for red, and YEARLY for yellow. Because both not analysed. The RT data were entered into a 2 x participants failed to show any effect in the word x Downloaded by [St Lawrence University] at 12:01 20 May 2016 3 (Word Type Congruency Condition) analysis naming task as a function of congruency, and also of variance. All painvise comparisons were done because we are interested in the extent of Stroop using Tukey post hoc comparisons at an alpha level interference in ink naming, we did not collect data of .05. for word naming in any of the subsequent experi- For the control subject, QK, an analysis of ments. This version of the task has the additional variance revealed a significant effect of word type benefit of removing further any interference from (standard, onset control), F(1, 203) = 21.2, p < serial processing of words as no word naming is .0001, a significant effect of congruency condition, involved in any of the conditions. F(2, 203) = 48.6, p i .0001, and a significant Stimuli were printed in capital letters in Aria1 interaction between the two factors, F(2, 203) = 48 pt font. The experiment was prefaced by 20.4, p < .0001. She did not show any significant instructions and a presentation of the colours used differences when comparing the control and con- in the task to ensure that the participants knew the gruent conditions for either standard words or

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onset control words (p > .05). Again, however, she (214.5 ms). Given that EL did not show a showed evidence of Stroop interference, with ink significant interference effect with the onset naming-incongruent (792.5 ms) significantly slower control words and that any interference obtained is than ink naming-control (588.9 ms), an increase of considerably less than the extent observed in the 203.7 ms (p i .05). QK did show interference to standard Stroop task, we can conclude that the some extent based on the first letters of the word, covert activation obtained in ink naming for EL is as shown by a longer mean RT in ink naming not merely a result of processing the first letter(s) onset-incongruent (633.8ms) compared to the ink of the word. naming onset-control condition (575.5 ms), a dif- ference of 58.2 ms (p < .05), but this was less than her interference seen in the standard Stroop task EXPERIMENT 4 (203.7 ms). This slight interference based on this first letter has been previously demonstrated in the In this experiment, we manipulated visual/percep- literature (see Macleod, 1981). tual aspects of the presented words by degrading An analysis of variance of EL'S data revealed a the stimuli in one condition and by displaying significant effect of word type, F(1,202) = 3 1.1,p < them in cursive font in another condition. The .0001, a significant effect of congruency condition, rationale for these manipulations stems from work F(2, 202) = 9.7, p < .0001, and no interaction. by Farah and Wallace (1991), who demonstrated There were no significant differences between the that a LBL patient was especially sensitive to control and congruent conditions (p > .05). EL stimulus degradation, as evidenced by the dis- demonstrated Stroop interference, with ink naming- proportionate increase in naming latency across incongruent (961.6 ms) significantly slower than word length when the words were masked. Farah ink naming-control (747.1 ms), an increase of and Wallace (1991) argued that serial letter-by- 214.5 ms (p < .05) (see Table 1). EL did show letter reading results from a deficit in perceptual an increase of 81.7 ms in RT from ink naming analysis of visual material and that visual changes onset-control to ink naming onset-incongruent; to the stimuli exacerbate the serial processing pro- however, this difference did not reach significance cedure. It is also the case that the performance of (p > .05) and is much less than her interference LBL readers is slowed, relative to normal subjects, seen in the standard ink naming condition as more visually complex fonts are used (Behrmann

Table 1. Response times (ms)for control and incongruent (Incog) Stroop conditions, and dgerence (Dzf incongruent-control) for Experiments 3-6 for EL and control subject QK

QK EL Downloaded by [St Lawrence University] at 12:01 20 May 2016 Control Incong Dzf Control Incong Dzf

Experiment 3 Normal 588.85 792.50 203.65 747.12 961.63 214.51 Onset control 575.53 633.75 58.22 628.48 710.16 81.68

Experiment 4 Degrade 577.13 678.58 101.44 731.25 765.94 34.68 Cursive 545.22 622.20 116.97 693.86 726.40 32.54 Experiment 5 Pseudohomophone 626.60 761.37 134.77 661.97 740.02 78.05 Experiment 6 Uncommon 604.83 687.94 83.11 703.20 757.77 54.57

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& Shallice, 1995), that visual similarity among EL showed no effect of congruency in the letters influences reading performance (Arguin & degrade condition (p > .05); however, she did Bub, 1993), and that the patients make predomi- exhibit an effect of congruency in the cursive con- nantly visual errors in their word reading. We are dition, F(1, 100) = 3.891,~< .024. Like QK, EL interested in whether this vulnerability to visual/ showed no difference in either the degrade or perceptual degradation was also evident in EL'S cursive condition when comparing control and covert word processing. congruent conditions. In contrast to QK's per- formance, EL did not show significant Stroop interference in either the degrade or cursive condi- Methods tion: There is an increase in RT from the control In the degrade condition, all stimuli were degraded to incongruent condition of 34.68 ms in the degrade using the PsyScope degrade function at a level of condition and 32.54 ms in the cursive condition, 0.7. This gives the appearance of random noise but this is not statistically significant (p >.05). overlaid on the stimuli, making identification more When orthographic manipulations are applied difficult. In the second condition, we presented all to the stimulus, EL no longer demonstrated covert words in cursive Swing 48 pt font. The two visual/ reading, as evidenced by the lack of Stroop inter- perceptual manipulation conditions were pre- ference. In contrast, the control subject QK still sented in separate sessions, each containing 108 showed robust Stroop interference, although this randomly presented trials with an equal number was not as great as in the standard Stroop task. from each of the three congruency conditions. All One possible explanation is that the alteration of other aspects of this experiment were the same as the visual input renders the stimuli too taxing on in the previous experiment. the processes used for word recognition. Conse- quently, in the time required to generate a response for ink naming, the written word is not sufficiently Results and discussion processed to exert an inhibitory effect on the We removed 1.4% of the data for QK and 3.7% for response when the colour and the word identity EL from the analysis because of naming errors, are incongruent. Because the normal subject is not failure of the microphone to trigger properly, or as dramatically affected by these orthographic because RT values were greater than 4 SDs from manipulations, she processes the written word fast the mean. Neither subject made more than two enough for it to have an adverse effect on ink naming errors in any of the conditions, so accuracy naming performance. EL, on the other hand, does performance is not analysed. The RT data were not have enough processing time on the word for entered into two separate one-way analyses of its output to have any influence on her speed of ink variance. All painvise comparisons were done colour naming. This experiment points out a

Downloaded by [St Lawrence University] at 12:01 20 May 2016 using Tukey post hoc comparisons at an alpha level limitation in the extent of covert activation in EL. of .O5. The control subject, QK, showed a significant effect of congruency in both the degrade, EXPERIMENT 5 F(2,103) = 16.2, p < .0001 and cursive conditions F(2, 104) = 22.6, p < .0001. In neither condition To determine whether EL has implicit access to was there a significant difference between the the phonological representation of words, in this control and congruent condition @ > .05; however, experiment we manipulated phonological aspects QK demonstrated a significant increase @ < .05) in of the presented words by using pseudohomo- RT in the incongruent compared to control con- phones of colour words. Prior studies (Montant & dition for both the degrade and cursive conditions, Behrmann, 2001) have demonstrated that EL does an increase of 101.4 ms and 116.9 ms, respectively benefit from being primed with pseudohomo- (see Table 1). phones, as measured by her decrease in naming

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latency for associated words; for example, having standard Stroop (Experiment 2 and 3) task. EL's seen a pseudohomophone prime, her RT is 200 ms apparent failure to show covert activation with a faster compared to being primed with an unrelated homophonically related prime also points to a nonword. Thus, in an explicit word reading task, boundary condition in her ability to process words she is able to derive strong enough phonological implicitly. representations and to be primed by related repre- We note that, on the right hemisphere account, sentations. the right hemisphere is capable of generating The pseudohomophone Stroop task has three lexical and semantic representations and, to a lesser conditions: a congruent condition which paired extent (if at all), phonological representations. In congruent ink colour and pseudohomophone (e.g., light of this, the reduced phonological Stroop BLOO in blue ink), an incongruent condition effect in EL might not necessarily be a good indi- (e.g., BLOO in red ink), and a control condition cator of right-hemisphere covert processing (even that was the same as in the previous experiments. though the task does not require word reading per The word stimuli consisted of WRED for RED, se) and so, in the next task, we return to an explo- BLOO for BLUE, GREAN for GREEN, and ration of lexical and semantic interference effects. YELOE for YELLOW. All other aspects of the design and procedures for this experiment were the same as in the previous experiments. EXPERIMENT 6

In this final experiment, we determine whether EL Results and discussion has implicit access to lexical-semantic representa- We removed from the analysis all error trials, tions of words. To do so, we examined her Stroop microphone trigger failure responses, and all trials interference from words less common than those in which all RT values exceeded 4 SDs from each used in the previous Stroop experiments. LBL subject mean. This resulted in a removal of 2.7% of readers, like normal subjects, are slower to name the data for QK and 1.8% for EL. The RT data words that are lower in frequency as compared to were entered into a one-way analysis of variance, higher in frequency, although frequency appears comparing congruency conditions. All painvise to interact with word length such that as length comparisons were done using Tukey post hoc increases, frequency effects are exaggerated comparisons at an alpha level of .05. (Behrmann et al., 1998). In this frequency Stroop The control subject QK showed a main effect of task, common colour words were replaced with condition, F(2, 101) = 26.5, p < .0001, with no words of the same length but of lower frequency. difference between control and congruent condi- The words used were TAN, PURPLE, BLACK, tions (p > .05). QK did demonstrate Stroop inter- and GRAY. The mean occurrence of common

Downloaded by [St Lawrence University] at 12:01 20 May 2016 ference, with an increase in RT of 134.8 ms in the colour words, as measured by Kusera and Francis incongruent condition compared to the control (1967), was 127.8 compared to 76.3 in the condition (p < .05) (see Table 1). uncommon colour word condition. All other EL showed a main effect of condition, aspects of the design and procedures for this F(2, 103) = 5.5, p < .005, with no difference experiment were the same as in the previous between control and congruent conditions @ experiments. .05). While EL's response times in the incongru- ent condition are 78.1 ms slower than in the Results and discussion control condition, this difference failed to reach significance @ > .05) and is considerably less than Two trials were removed from EL's analysis, one the amount of Stroop interference seen in QK. for a naming error, and the other because of micro- This amount of interference is also much reduced phone trigger problems, resulting in a removal of relative to the extent of EL's interference in the 1.8% of the data. Neither subject had responses

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that exceeded 4 SDs from each subject mean. QK processing and, even when they do, the extent and did not have any data removed because there were nature of the implicit representation is not partic- no naming errors or microphone trigger problems. ularly well understood. While some researchers The data for each subject were entered into a one- have suggested that this covert processing gives rise way analysis of variance, comparing conditions. All to rich and detailed representations, others have painvise comparisons were done using Tukey post argued that this is not so and that the representa- hoc comparisons at an alpha level of .05. tion is, at best, partial and imprecise. On this latter QK showed a main effect of congruency, account, the failure of the patients to explicitly F(2, 105) = 17.17, p < .0001, with no difference identify the word is a direct consequence of the between the control and congruent conditions (p > partial and impoverished representation, which .05). QK demonstrated Stroop interference, with arises from the residual function of the normal an increase of 83.11 ms from the control condition reading system. to the incongruent condition (p < .05) (see Table We have adopted a Stroop interference para- 1). However, this interference is less than that she digm with a LBL patient, EL, with two major exhibited to the more common words (Experiment goals. The first is to explore whether, using a pro- 2, 261.2 ms; Experiment 3, 203.7 ms). This cedure in which subjects are required to name the reduction in Stroop interference is compatible with colour of the ink of a letter string without reading the results reported in the literature (Macleod, the word, we can elicit evidence of covert process- 1991). ing in an individual who does show some covert EL also showed a main effect of congruency, processing in the more standard implicit tasks F(2,103) = 3.077,~< .05. There was no significant (such as lexical decision and binary semantic clas- difference between the control and congruent con- sification) although this is not as strong as that dition (p > .05). EL failed to show Stroop interfer- observed in some other LBL readers (see Coslett ence, with a 54.6ms increase from the control to & Saffran, 1989). The critical finding is that this the incongruent condition @ > .05). This is much procedure, which does not engage word rec- less compared to the Stroop interference seen in ognition (and serial processing), produces Stroop common colour words (Experiment 2, 194.5 ms; interference in EL of the same magnitude as in Experiment 3, 214.5 ms). This difference is also the matched control subject. Moreover, as with the less than the interference effect seen in QK, which control subject, when only the first letter(s) of was statistically significant. the word matches the colour name, very little interference is obtained, indicating that more than the first letter must be activated implicitly in order GENERAL DISCUSSION to give rise to the Stroop interference effect. The implication of this is that EL must be processing Patients with pure alexia, also known as LBL Downloaded by [St Lawrence University] at 12:01 20 May 2016 more than the first letter of the word covertly. readers, read in a laborious and sequential manner, The second goal is to explore the nature and as is evident in their increase in naming latency as extent of the representations that are activated a function of the number of letters in a word covertly. To this end, we explore whether the string. However, counterintuitive and perplexing Stroop interference is of the same magnitude as in evidence has amassed showing that some of these the normal reader when we manipulate various patients do in fact exhibit some level of covert aspects of the word stimulus in relation to the reading in which words are processed rapidly and colour of the ink. Understanding this will allow us perhaps even in parallel. Indeed, under some cir- to determine the extent of the orthographic, cumstances, the patients appear to have considera- phonological, and semantic activation that is ble information about a word (for example, its possible at an implicit level in a LBL reader. We semantic category) despite being unable to identify found that, first, the extent of the Stroop inter- it explicitly. But not all patients show this covert ference is reduced in the matched control subject

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under these various conditions but that in all cases, be weaker or less precise than that activated by a she still showed a significant difference between normal control and so this underlying representa- ink naming speed in the control versus the incon- tion may not be sufficiently robust to support word gruent condition. Second, and perhaps more naming, which requires precision. relevant, EL did not show Stroop interference Before discussing the theoretical implications of when the written words are less frequent than the these findings, we need to point out that we are not common colour words, when the written words are the first to run a Stroop experiment with a LBL degraded or presented in cursive font, or when the reader: Patterson and Kay (1982) ran a Stroop written words are homophonically related to the experiment using ink naming with one of their colour word. LBL readers, MW, but obtained no evidence of That we observe Stroop interference in only Stroop interference. Surprisingly, and in contrast some conditions for EL, in contrast with the with our results, they observed a congruency effect control subject, suggests that while some aspects of (better performance on congruent than control the written word are activated, not all aspects are condition); however, as we suggest below, they too adequately represented to support covert process- argued that this covert facilitation might arise from ing. Many interpretations of the interference effect partial processing of the word. The absence of an in Stroop tasks rely on the finding that word interference effect in their patient, however, is reading proceeds at a faster pace than ink naming somewhat surprising given that we have claimed (due to the increased experience with word read- that it is a particularly useful paradigm, which does ing) and, hence, the processed written word can not evoke sequential processing of letters. That adversely impact the ink naming when the outputs MWdid not show this effect may suggest that this are incongruent (see, for example, J. D. Cohen, might not be as watertight and robust a procedure Servan-Schreiber, & McClelland, 1991). The as we have proposed. Alternatively, it may still be presence or absence of the Stroop effects in EL, possible that even if the procedure is robust, covert then suggests that in the amount of time the word word reading might not be evident in all individu- is present before the ink colour is read, only a als. In particular, because MW was so severely limited amount of word processing can be com- impaired (she took 12.8 seconds to read a three- to pleted. It is only the standard Stroop task, in which four-letter word), covert effects may not be possi- word processing conditions are ideal and the most ble in very profoundly impaired LBL readers. information can be extracted from the word, which These suggestions are speculative, however, and may offer sufficient time for word processing for remain to be explored further. EL. We also note that in the standard Stroop task, As mentioned previously, one prominent theory only a small number of highly common words are about pure alexia argues for two different modes of used and this, too, can facilitate the speed of word word processing: a right-hemisphere based parallel mode that is the source of covert processing, and a Downloaded by [St Lawrence University] at 12:01 20 May 2016 processing in EL. But of great relevance is that manipulating aspects of the word, including left-hemisphere based sequential mode that is the frequency, visual input, or the relationship between source of the laboured serial reading pattern. Given orthography and phonology, no longer provides that covert processing is mediated by the right sufficient time for word processing and the auto- hemisphere and that the letters are processed in matic inhibition of ink naming in the incongruent parallel, one might expect that the extent of this case. In sum, when all components of the word are covert activation would be normal (the hemisphere favourable (high frequency, small set of items, is intact) if it is not subject to any interference by accessible font, consistent phonology and seman- the sequential word process that usually opposes it. tics), enough factors can combine to activate a The alternative perspective does not differentiate covert representation that can influence ink between two modes of processing and presupposes naming. When one explores further, however, the that all forms of reading emerge from the residual representation that is activated covertly is found to function of the normal reading system, which has

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been damaged. Any covert processing, then, will was independent of word length. The authors con- reflect whatever activation the system is capable clude that a decreased naming latency for words of generating given the exposure duration of with many orthographic neighbours is evidence for the stimulus and it will probably be partial and an intact parallel letter processor. However, unlike imprecise. controls, IH was slower at naming words that con- Given the abnormal covert activation observed tained many versus a few conhsable letters (i.e., a in EL, the findings seem more compatible with the similarity of letters within a word with other letters latter perspective of a single, integrated, reading of the alphabet). The claim is that parallel letter system. This perspective has been fleshed out in processing may still be possible but that it gives rise some detail recently by Behrmann and colleagues to considerable background noise and that this (Behrmann et al., 1998b; Montant & Behrmann, noise prevents the system from resolving differ- 2001). This view holds that a general visual ences between visually similar letters. It is this perceptual deficit, which degrades the quality of noise that makes the sequential processing of the input, sustained by virtue of the left posterior letters mandatory. The relevant aspect of this is hemisphere damage, is fundamental to LBL read- that the parallel activation that arises is simply too ing. As a result of this perceptual deficit, only weak weak and it is possible that it may only support parallel activation is possible and, to increase this rudimentary covert processing. activation, patients need to make multiple fixations Consistent with this is the claim by Osswald, to allow the higher spatial resolution of the fovea to Humphreys, and Olson (2002) that attempts to be applied to the input. Indeed, a recent study has read at the supra-letter level (in parallel even if to a documented that LBL readers make more frequent limited extent) has detrimental consequences for fixations on longer than shorter words than do word recognition in LBL readers. Their patient, normal readers (Behrmann, Shomstein, Black, & DM, who appears to be very similar in severity to Barton, 2001). Any covert effects emerge from EL as defined by the slope of the naming latency whatever weak parallel activation is possible under function (roughly 400 ms in both cases), per- the limited exposure duration used for stimulus formed better when letters were presented sequen- presentation. tially than simultaneously. The interpretation of The notion that there may be some parallel this is that simultaneous letters give rise to activation, which is weak and insufficient to increased lateral masking and disrupt the extrac- mediate reading, also derives support from several tion of individual letters. Interestingly, DM also very recent studies on the topic. Lambon Ralph, performed better when a few letters, corresponding Hesketh, and Sage (2004 this issue) present data to a fimctional spelling unit, are presented at a time from pure alexic patient FD, who demonstrated than under simultaneous conditions, suggesting decreased performance in a brief presentation that some supra-letter processing is possible but lexical decision and semantic categorisation task that it breaks down when larger units are pres- Downloaded by [St Lawrence University] at 12:01 20 May 2016 as a function of decreasing word frequency, image- ented. Again, the relevant finding here is that ability, and familiarity. These data led the authors parallel activation of visual input may not only be to conclude that FD's fast access to lexical and too weak but can also be detrimental. semantic aspects of words is evidence for a weak The data from FD, IH, and DM, like EL, parallel activation of words: however, this is suggest that parallel activation of many letters is insufficient to drive normal word processing, not sufficiently strong to mediate covert process- which is the reason for the severe LBL reading. ing. Rather, the output of these individuals suggest Arguin, Fiset, and Bub (2002) demonstrated that there may be some limited parallel activation, that their LBL reader IH, like controls, was faster which is insufficient and which compels a sequen- at naming words that had many as compared to tial procedure. Rather than thinking about two few orthographic neighbors (i.e., words of the independent reading routes, then, the findings same length that differ by one letter) and that this from EL might more profitably be explained as

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