STUDIA PSYCHOLOGICA, 55, 2013, 1 67

SERIAL POSITION AND DISTANCE EFFECTS IN VISUAL WORKING MEMORY

Barbara DOLENC1, Jurij BON1, Grega REPOVŠ2

1 Department of Neurology, Laboratory for Cognitive Neuroscience University Medical Centre Zaloška 2, 1000 Ljubljana, Slovenia E-mail: [email protected]

2Department of Psychology, Faculty of Arts University of Ljubljana Aškerčeva 2, 1000 Ljubljana, Slovenia

Abstract: Numerous studies have identified and explored the factors that affect order information processing in verbal working memory (WM), whereas little is known about order maintenance in visual WM. To gain better insight into the possible mechanisms of representing order in visual WM, we assessed the extent of serial position and item distance effects on visual WM. 20 students performed a visual WM task. They were asked to encode and maintain either the identity or temporal order of four visual stimuli. The results revealed recency and distance effects congruent with previous studies of verbal WM, however, no primacy effect in accuracy results was detected. Distance was revealed to be closely intertwined with recency, making it difficult to estimate their separate effects on order recognition. These results suggest that order coding in visual WM involves the use of a magnitude of codes similar to those employed in number processing and verbal WM.

Key words: visual working memory, temporal order memory, primacy, recency, distance effect

Working memory (WM) is a key compo- goal-oriented plans is coding and mainte- nent of human cognition, enabling mainte- nance of order information. nance of information relevant for the execu- WM, as most researchers agree, is not a tion of the ongoing task. WM consists of unitary system. The multicomponent model short-term memory stores that can tempo- of WM (Baddeley, 2000; Baddeley, Hitch, rarily hold a limited amount of information in 1974) - probably the most influential cogni- an easy accessible state (Atkinson, Shiffrin, tive model of WM - identifies four separate 1968; Baddeley, Hitch, 1974) and processing components: a phonological loop that en- mechanisms that help make use of the short- ables storage of verbal information; a visuo- term memory (Cowan, 2008). WM should spatial sketch-pad dedicated to maintenance therefore be distinguished from short-term of visual and spatial information; an episodic memory as it refers to structures and pro- buffer storing integrated multimodal infor- cesses used not only for temporary storage mation and providing link to long-term of the information but also for manipulation memory; and a central executive, controlling of the stored information. A key feature of access to and manipulation of information WM that enables formation and control of within WM. Each of the components may

DOI: 10.21909/sp.2013.01.622 68 STUDIA PSYCHOLOGICA, 55, 2013, 1 depend on separate mechanisms and pro- hearsal, thus increasing their probability of cesses for encoding and maintenance of in- recall. Craik and Lockhart (1972) hypoth- formation. Of these, much attention has been esized that items at the beginning of the list paid to representations and processes that are subject to elaborative processing in or- enable maintenance of order information in der to allow rehearsal of items presented sub- verbal WM, however, surprisingly little is sequently. Another account claims that early known about how order is coded and main- list items simply receive enhanced attention tained in visual WM. resources and, consequently, are better en- Identifying the factors that affect and coded regardless of how many additional shape cognitive abilities is a necessary step rehearsals they receive (Neath, Crowder, towards proposing and validating specific 1990). Recency effects, in contrast, occur models and theories about mechanisms and because the words at the end of the list are representations that enable them. In the still being held in short-term memory study of verbal WM three empirical findings (Rundus, 1971). This view is consistent with seemed to be particularly influential the dual-store models, in which late list items (Marshuetz, 2005): serial position effects, are retrieved from a highly accessible short- distance effect and error types in serial re- term memory store (Raaijmakers, Shiffrin, call. The focus of this paper will be the serial 1981). Both, primacy and recency can be ex- position and distance effects. plained with the feature of distinctiveness, the degree to which a given item stands out Serial Position Effect among the other items in the set (Neath, 1993). This view of distinctiveness can pre- Shortly after learning a list of items, the dict the shape of the serial position func- subjects’ recall or recognition performance tion: the most recent to-be-remembered items usually depends on the serial position of the and the first few items in a uniformly spaced item in a predictable way. Items in the first list are temporally more distinct than the and the last positions are often better remem- middle items. bered than the ones in the middle of the list, as indicated by higher accuracies and shorter Distance Effect reaction times (e.g., Golob, Starr, 2004; Jones, Polk, 2002; Lange, Cerella, Verhaeghen, 2011; Distance effects are typically noted in McElree, Dosher, 1989; Sederberg et al., 2006; tasks requiring subjects to make relative judg- Stephane et al., 2010; Talmi, Goshen- ments about an aspect of two stimuli that are Gottstein, 2006; Williams, McCoy, Kuczaj, definable along some dimension, such as 2000; Zhang et al., 2003). The superior physical size. For example, the time to judge memory for the first item has been termed the distance between items in perceived spa- the primacy effect, and for the last item, the tial arrays is shorter for items that are farther recency effect. apart (Holyoak, 1977). The same effect is Some authors (e.g., Baddeley, 1986; observed in judgments about imagined real- Rundus, 1971) have suggested that the first world objects, for which, for example, a few items from the to-be-remembered list rep- subject’s response to the question of which resented the benefit from the greatest re- object is larger is faster the more disparate STUDIA PSYCHOLOGICA, 55, 2013, 1 69 their sizes (Moyer, 1973). Distance effect is As for the distance effect, all previous stud- also observed in the order of letters (e.g., ies were done on pairs of strings of letters Angiolillo-Bent, Rips, 1982; Proctor, Healy, (Angiolillo-Bent, Rips, 1982; Proctor, Healy, 1987) and in numerical comparisons (Buckley, 1987) or numbers (Buckley, Gillman, 1974; Gillman, 1974; Dehaene, Dupoux, Mehler, Dehaene et al., 1990; Milosavljevic et al., 2011), 1990; Milosavljevic et al., 2011). Size and dis- whereas, to our knowledge no such studies tance effects in numerical cognition have exist on visual stimuli nor on visual WM. inspired the proposal that we cognitively Based on verbal WM empirical findings, represent numbers on a mental number line several possible mechanisms of represent- (Restle, 1970). In this view, numerical dis- ing order information have been proposed. tance is expressed as spatial distance, and The first possibility is that items are coded similarity in number size is captured as rep- with respect to other items on the list via resentational overlap (Göbel, Shaki, Fischer, inter-item associations (e.g., Henson, 1999; 2011). This phenomenon implies that repre- Marshuetz, 2005). When probed with two sentation of size and quantity are stored as items that were on the list and asked to make magnitudes that are easier to discriminate a judgment about whether the items appear from one another if more disparate (Chochon in the same order as they were presented in et al., 1999; Marshuetz et al., 2000). the list, this inter-item associative mechanism predicts that reaction time will increase with Coding of Order in Visual WM the number of intervening items (Marshuetz et al., 2000). The second possible mechanism Whereas order effects have been exten- for coding order information is an explicit sively studied in verbal WM, studies of vi- association of temporal or ordinate position sual WM are few and far between. In hu- to each item (e.g., Anderson, Matessa, 1997). mans, primacy and recency effects are ob- We refer to this possibility as direct coding. served in various studies using verbal The behavioral prediction for a direct cod- stimuli, such as numbers (e.g., Golob, Starr, ing model differs from that of an inter-item 2004; Zhang et al., 2003), letters (e.g., Henson association model: If response time is mea- et al., 2003) or words (e.g., Jones, Polk, 2002; sured to a pair of probes it should not vary Murdock, 1962; Rushby, Barry, Johnstone, with the distance between the items in the 2002; Sederberg et al., 2006; Stephane et al., list because subjects can access the associ- 2010; Talmi et al., 2005). Studies of primacy ated position for each item and then com- and recency effect in visual WM (Roberts, pare which of those position codes is larger Kraemer, 1981; Woodman, Vogel, Luck, 2012; (Marshuetz, 2005). The third possible order- Wright et al., 1985) are rare and mostly in- coding mechanism is one in which the tem- volve animal subjects. The studies report of poral position of an item is represented on a no primacy and substantial recency effect continuous scale of a variable, such as an with short retention intervals, however, as index of item recency, familiarity, or some the retention interval increased, the magni- other code that can be expressed in magni- tude of primacy effect increased while that tudes (e.g., Brown, Preece, Hulme, 2000; of the recency effect decreased (Wright et Neath, Crowder, 1990). To the extent that al., 1985). items in memory are coded according to mag- 70 STUDIA PSYCHOLOGICA, 55, 2013, 1 nitude information, the behavioral data should parallel psychophysical functions for Materials and Design other perceptual judgments, such as size dis- criminations, which are also thought to be The participants completed a visual WM coded in terms of magnitude. That is, the task in which their task was to remember ei- more the items are separated in time, the easier ther the identity or the order of four sequen- the judgment of their temporal order should tially presented items. The length of the se- be (Marshuetz, 2005). quence was chosen, as empirical evidence To our knowledge, no study exists that suggests that visual WM is limited to ap- would relate the proposed mechanisms of proximately four items (Luck, Vogel, 1997; order coding to visual WM and explicitly test Pashler, 1988). Using four items allowed us them. That is what our study aimed to ad- the study of order effects and, at the same dress. Our goal was to explore the presence time, ensured that the participants were able and extent of order related effects - serial to encode and remember the items on most position and distance - on visual WM, com- trials. Sequential rather than simultaneous pare them to verbal WM findings, and test presentation was used, as previous studies the predictions of the three proposed mecha- (Blalock, Clegg, 2010; Jiang, Olson, Chun, nisms of order coding. Three possibilities 2000) suggest that sequential presentation were explored. First, an increase in reaction isolates each item during the encoding, times of order judgments with increased in- whereas simultaneous presentation encour- ter-item distance would support the predic- ages the use of spatial configuration over an tions of inter-item association coding. Sec- item-focused representation. Using sequen- ond, no effect of inter-item distance on order tial presentation we ensured that the items judgment reaction times would best fit the were encoded individually in visual WM. In direct coding of order in visual WM. Third, a addition, presenting them at the same loca- decrease of reaction time and increase in ac- tion prevented recoding an order task into a curacy of order judgments with increase of spatial position task. inter-item distance would suggest that order To enable additional analyses that are not information in visual WM is represented the focus of this paper, in each trial two se- using magnitude coding. quences of stimuli were presented, one to the left and one to the right visual hemifield METHODS with the participant having to attend to and remember only one of them. The laterality of Participants the stimuli to remember was varied randomly within each block of trials. 20 students from University of Ljubljana The progression of the task is illustrated participated in the study (15 females, 5 in Figure 1. Each trial started with a cue stimu- males). Mean age of participants was 23.71 lus indicating the type of the trial and the years (SD = 2.14 years). All the participants side of the display that the participant should had normal or corrected to normal vision. All attend to. The participants were asked to participants gave written informed consent encode and maintain either the identity (Item prior to participation in the experiment. condition) or temporal order (Order condi- STUDIA PSYCHOLOGICA, 55, 2013, 1 71 tion) of the items that were presented in the decay to the point of being unusable. Stimuli indicated hemifield. The cue was presented traces were additionally attenuated by lower for 700ms and followed by a 300ms presen- contrast between the letter and background tation of the fixation cross. In the encoding (dark blue on medium gray). The timing struc- phase of the trial four pairs of stimuli were ture therefore enabled the participants to in- presented sequentially. In each pair, one dividually encode each presented item, with stimulus was presented on the left and the no or minimal sensory trace interference. other on the right side of the fixation point. After the encoding phase, a 3500 ms delay Each pair was presented for 800 ms with 300 (maintenance phase) followed before a probe ms inter-stimulus interval (ISI). During the appeared on the screen. Subjects were in- presentation the participants were asked to structed to look at the fixation point on the look at the fixation cross while observing the screen during the delay phase. After the de- stimuli in their lateral visual field. According lay the probe consisting of two stimuli ap- to previous studies (e.g., Phillips, 1974), with peared. In the order condition, participants ISI of 100 ms or longer, stimuli sensory traces had to indicate by pressing a button, which

Figure 1. Schematic diagram of the visual WM paradigm. Each trial started with a cue indicating the task and the hemifield to attend to. Four visual stimuli were then sequen- tially presented in each hemifield. After a delay, a probe was presented to which partici- pants responded by pressing a key indicating the stimulus that appeared in the original set (item condition) or the stimulus that appeared first in the original set (order condition). Arrows indicate the correct response for each of the conditions. 72 STUDIA PSYCHOLOGICA, 55, 2013, 1 of the two items was shown earlier in the the examination of distance effects, target sequence. In the item memory trials, the test probes in Order condition were either 0 items display consisted of one item from the apart (adjacent items, distance 1), 1 item apart memory set, along with a visually similar foil (one intervening item between probes, dis- item. Participants had to indicate by press- tance 2) or 2 items apart (two intervening ing a button, which of the presented items items between probes, distance 3). All three was a part of the initial set. Each trial was distances occurred with equal frequency. followed by 1700 ms inter-trial interval (ITI). The stimuli were presented on a 19" CRT During the ITI the subjects were instructed screen. At a distance of 100 cm they were to look at the fixation cross until the cue for approximately 3.4° in size and were presented the next trial appeared. with 8.1° eccentricity. The task was con- Visual stimuli were letters of 129 different trolled by E-Prime (Psychology Software font types. The stimuli were carefully cho- Tool, Pittsburgh, PA) running on a Windows sen based on prior piloting with the aim to XP operating system. The participants pro- reduce the possibility of verbal recoding. As vided their responses by pressing either left the identity of the letters within a sequence of right mouse button using their dominant remained the same, their verbalization did not hand. provide any task relevant information to the participant. Additionally, the letters differed Procedure in a number of nonpredictable features that were difficult to verbalize, which further re- Participants were comfortably seated, view- duced the possibility of successful use of ing the computer screen at a distance of verbal recoding strategies. By making sure 100 cm. The task started with presentation that on each trial the identity of the letters of written instructions. First, participants car- used in the target hemifield differed from the ried out a practice block to familiarize them- letters in the opposite visual hemifield as well selves with the experiment. Participants con- as letters used in the previous trial, the choice tinued with the task only after the experi- of stimuli enabled us to minimize the poten- menter made sure that they understood the tial of interference from either set of stimuli. instructions. The different types of each letter were The task was organized in 10 blocks of 40 grouped in 12 different clusters based on trials each. Each block consisted of 20 Item their visual similarity. To ensure the distinc- and 20 Order trials presented in random se- tiveness between items, the letters for the quence in order to reduce the possibility of memory set were chosen from four different developing task specific strategies. Similarly, randomly selected clusters. Conversely, to the side of the target stimuli as well as the make the Item condition more challenging, stimuli (letters) used changed randomly from the foil probe in the Item condition was se- trial to trial and were balanced across both lected from the same cluster as the probe Item and Order trials. Each block took ap- from the initial set. proximately 9 minutes to complete. Blocks On Item trials, the probe had an equal were separated by short breaks to give par- chance of occurring at any serial position ticipants the opportunity to rest before con- (first, second, third or fourth). To allow for tinuing with the task. In sum, each partici- STUDIA PSYCHOLOGICA, 55, 2013, 1 73 pant completed 200 Item and 200 Order tri- als. In each trial reaction times and accuracy RESULTS of responses were recorded. Participants were asked to focus on the visual details of Serial Position the letters and avoid trying to verbalize their features. Post-test debriefing indicated that To explore the effect of serial position on the participants were not able to and did not accuracy in Item condition we computed re- try to use verbal recoding strategies. peated-measure one-way ANOVA with item Differences in accuracy and reaction times position (1, 2, 3 or 4) as the single factor. The between different serial positions and item results (see Figure 2) confirmed a significant distances were analyzed using one-way effect of serial position (F(3, 16) = 11.63; p < 2 2 ANOVA for repeated measures and ηp ef- .001; ηp = 0.45). Post-hoc analyses revealed fect size was computed. When significant, significantly better accuracy when the the effects were further explored using post- probed item was presented last in compari- hoc analyses with Bonferroni correction for son with position 1 (t(19) = -5.05; p < .001; multiple comparison and computation of d = -1.34), position 2 (t(19) = -3.34; p = .005; Cohen’s d effect size. d = -1.06) and position 3 (t(19) = -4.58; p <

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0 I1 I2 I3 I4 Item position Figure 2. Accuracy as the function of serial position of the target item in Item condition. Error bars represent standard errors. * p < .0125 74 STUDIA PSYCHOLOGICA, 55, 2013, 1

.001; d = -1.22). No other effects passed sta- tistical significance. Distance Next, we also tested the effect of serial position on reaction times in correct trials. To assess the effect of distance on accuracy To avoid outliers, all reaction times that dif- of order judgments we computed repeated- fered more than 2 standard deviations from measure one-way ANOVA with item distance the mean in each condition were excluded (1, 2 or 3) as the single factor. ANOVA showed from the analysis prior to computing each a significant effect of distance on accuracy 2 subject’s averages. Repeated-measures one- (F(2, 16) = 27.13; p < .001; ηp = 0.66). Post-hoc way ANOVA revealed a significant effect of analyses revealed that subjects performed 2 serial position (F(3, 16) = 6.83; p = .001; ηp = significantly worse with adjacent items than 0.33). Post-hoc analyses revealed slower re- when items were one (t(19) = -3.93; p = .002; action times when probed item was presented d = -1.04) or two (t(19) = -2.44; p < .001; d = in position 3 in comparison with position 1 -1.44) items apart, however, differences be- (t(19) = -3.30; p = .005; d = -0.24) and with tween the latter two cases did not reach sig- position 4 (t(19) = 3.53; p = .003; d = 0.61). nificance (t(19) = -2.44; p = .028; d = -0.64). For Results are presented in Figure 3. results see Figure 4.

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1400 I1 I2 I3 I4 Item position Figure 3. Reaction time as the function of serial position of the target item for correct responses in Item condition. Error bars represent standard errors. * p < .0125 STUDIA PSYCHOLOGICA, 55, 2013, 1 75

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Figure 4. Accuracy as the function of distance of target items and serial position within specific distance in Order condition. Lines connect mean accuracy at each of the distances. Error bars represent standard errors. Dashed lines represent statistical significance for the main effect of distance, whereas filled lines represent statistical significance within specific distance. * p < .0167

To identify the possible mediating effect .018; d = -0.68), and 3 and 4 (t(19) = -3.37; p = of serial position we also analyzed the effect .005; d = -0.93). The difference between the of serial position on accuracy in order judg- later two did not reach significance (t(19) = ment. A repeated-measure one-way ANOVA -1.60; p = .133; d = -0.51). Similarly, when with positions within distance 1 as a single probes were spaced one item apart (distance factor (positions 12, 23, and 34) confirmed a 2) accuracy was significantly worse when significant serial position effect on accuracy probes were shown in serial positions 1 and for order judgment on adjacent items 3 in comparison with positions 2 and 4 2 (F(2, 16) = 6.73; p = .004; ηp = 0.33). Post-hoc (t(19) = -3.16; p = .007; d = -0.94). analyses revealed that accuracy was signifi- To control for the effect of serial position, cantly worse when probes in Order condi- we then compared accuracy across distances tion were in serial positions 1 and 2 com- only for those cases when one of the probed pared to positions 2 and 3 (t(19) = -2.68; p = items was presented in the most memorable, 76 STUDIA PSYCHOLOGICA, 55, 2013, 1 last position (items 3, 4 vs. items 2, 4 vs. items for correct responses that did not deviate 1, 4). The results showed significant main more than two standard deviations from the effect of distance on accuracy (F(2, 16) = 6.20; mean in each condition were used to com- 2 p = .006; ηp = 0.31). Post-hoc analyses re- pute subjects’ averages. Repeated-measures vealed better accuracy for distance 3 in com- one-way ANOVA again confirmed a signifi- parison to distance 1 (t(19) = 3.78; p = .002; cant effect of item distance (1, 2 or 3) on d = 0.79). The same trend was observed for reaction times (F(2, 16) = 42.87; p < .001; 2 the difference between distances 1 and 2, ηp = 0.75, see Figure 5). Post-hoc analyses however, the effect did not reach the more revealed that reaction times were signifi- stringent statistical threshold (t(19) = 2.52; cantly shorter with larger distances for all p = .025; d = 0.77). There was practically no cases, comparing distances 1 and 2 (t(19) = difference between distances 2 and 3 (t(19) = 3.12; p = .008; d = -1.04), distances 1 and 3 -0.18; p = .86; d = -0.06). (t(19) = 7.45; p < .001; d = -1.44) as well as Next, we tested the effect of item distance distances 2 and 3 (t(19) = 6.97; p < .001; d = on reaction times. Again, only reaction times -0.64).

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Figure 5. Reaction times for correct responses as the function of distance of target items and serial position within specific distance. Lines connect mean reaction times within each distance. Error bars represent standard errors. Dashed lines represent statistical signifi- cance for the main effect of distance, whereas filled lines represent statistical significance within specific distance. * p < .0167 STUDIA PSYCHOLOGICA, 55, 2013, 1 77

Again we tested for possible serial posi- coding mechanisms (inter-item association, tion effects. Repeated-measures one-way direct coding and magnitude coding) best ANOVA indeed revealed significant effect of describes maintenance of order information serial position on reaction times for adjacent in visual WM. We focused specifically on 2 probes (F(2, 16) = 18.98; p < .001; ηp = 0.58). serial position and distance effects. Post-hoc analyses revealed that the items in position 3 and 4 required shorter reaction Serial Position Effect times than items in positions 1 and 2 (t(19) = 3.43; p = .004; d = 0.61) and position 2 and 3 The results from the Item condition re- (t(19) = 6.13; p < .001; d = 0.96), whereas the vealed different patterns of accuracy and difference in reaction times between posi- reaction times as a function of probe posi- tion 1 and 2 vs. position 2 and 3 did not reach tion with the domination of recency effect. significance when Bonferroni correction was The results demonstrated significantly bet- applied (t(19) = -2.73; p = .016; d = -0.52). ter accuracy and faster reaction times when Similarly, when items were 2 positions apart, the probe was from the end of the initial set the reaction times were shorter when the in comparison with all other positions (see probes were shown on positions 2 and 4 in Figures 2 and 3), which is consistent with comparison with positions 1 and 3 (t(19) = the recency effect. According to the distinc- 3.44; p = .004; d = 0.73). tiveness theory (Neath, 1993) it seems that To control for the effect of serial position the most recent to-be-remembered items we again compared distances on only those stand out among the other items in the set cases that included the most memorable and are temporally more distinct in compari- fourth item. Repeated-measures one-way son with items from the middle and, in our ANOVA with factor distance (3 and 4 vs. 2 case, also from the beginning of the list. Our and 4 vs. 1 and 4) showed significant main accuracy results did not reveal any primacy effect of distance on the reaction times effect, as the stimuli from the beginning of 2 (F(2, 16) = 8.03; p = .002; ηp = 0.36). Post-hoc the list were not better recognized. However, analysis revealed faster reaction times for dis- reaction times for the first three items did tance 3 in comparison with distance 2 increase with the position, congruent with (t(19) = -5.07; p < .001; d = -0.54) and dis- the primacy effect. tance 1 (t(19) = -3.09; p = .008; d = -0.43). The observed pattern of strong recency However, there was no significant difference and absent primacy effect in accuracy data between distance 1 (item position 3 and 4) differs from findings reported in studies of and distance 2 (item position 2 and 4) (t(19) = verbal WM, which show the influence of -0.05; p = .960; d = 0.01). both recency (e.g., Golob, Starr, 2004; Stephane et al., 2010; Talmi, Goshen- DISCUSSION Gottstein, 2006; Talmi et al., 2005), as well as primacy effect of serial position on recall ac- The aim of our study was to determine to curacy (e.g., Jones, Polk, 2002; Sederberg et what extent visual WM exhibits similar order al., 2006; Stephane et al., 2010; Williams et al., related effects as verbal WM, and more spe- 2000). A number of possible explanations of cifically, to test which of the proposed order the observed discrepancy can be considered. 78 STUDIA PSYCHOLOGICA, 55, 2013, 1

First, significant primacy effect is usually Third, as no visual masking was used be- found in intentional learning tasks, and likely tween trials, a week primacy effect could reflects the subjects’ use of elaborative re- also be explained by interference between hearsal strategies to help associate items and the trace of the probe from the previous encode them into memory (Craik, Tulving, trial and the first target stimulus of the fol- 1975). Such elaborative rehearsal strategies lowing trial. As visual WM is limited in ca- (e.g., making a story out of the list items) pacity and is quickly updated with new vi- result in increased rehearsal of early list items sual input, it would be advantageous to during later item presentations (Tan, Ward, maintain only currently relevant information 2000), and consequently relatively poorer (Makovski, Jiang, 2007). However, recent encoding of items later in the list. One pos- studies report that one cannot fully elimi- sible reason for the lack of primacy effect in nate unwanted visual information from the our study could be due to the differences in current WM tasks (Makovski, Jiang, 2008). the rehearsal mechanism between verbal and The use of different letters in the consecu- visual WM, the latter not allowing for the tive trials makes the stimuli clearly distinct same kind of elaborative strategies as the and should significantly reduce the possi- former. The dependence of primacy effect on bility of such interference, its possible ef- rehearsal strategies afforded by phonologi- fect, however, should still be addressed in cal loop was demonstrated in a verbal WM future studies. study by Baddeley and Hitch (1974), show- Last, a number of studies have demon- ing that a concurrent task engaging the pho- strated a capacity limit of visual WM of only nological loop significantly impairs recall about three to four items (e.g., Alvarez, accuracy for earlier serial positions, however, Cavanagh, 2004; Luck, Vogel, 1997; Pashler, it does not reduce the recency effect. 1988). Taking that into account, it seems Second, the few existing studies of visual likely that better recall of the last items in a WM that explored the serial position effect series is a consequence of overwriting the in visual WM (Roberts, Kraemer, 1981; memory for prior items by subsequent items Wright et al., 1985) report significant effect (Glanzer, Cunitz, 1966). As suggested by of delay period on serial position curve. The Woodman et al. (2012) who obtained a simi- effect was most convincingly shown in the lar pattern of results, these might reflect the study by Wright et al. (1985), in which only capability to dynamically update the content recency effect was observed in the shortest of visual WM and displace earlier items once delays (0 and 1s) and only primacy effect the capacity limit was exceeded. remained at the longest delay (100s), whereas The last interpretation is also most con- both were present in the medium delay gruent with the obtained reaction time re- lengths. The authors attributed the findings sults that show both recency and primacy to differential time courses of fast decaying effect. Namely, when the items from the be- retroactive interference and slow growth of ginning of the list do remain in memory, the proactive interference. From that perspec- earlier ones do have the distinctiveness ad- tive, it could be argued that the 3.5s delay vantage over the following ones, leading used in our study was too short to elicit pri- to faster reaction times for accurate re- macy effect. sponses. STUDIA PSYCHOLOGICA, 55, 2013, 1 79

actly what has been observed in our results, Distance Effect which therefore support the hypothesis that temporal position of items in visual To differentiate between different possible WM is represented using a magnitude code, mechanisms of order coding in visual WM, similarly to representation of size and quan- we also investigated the presence and char- tity (Chochon et al., 1999; Marshuetz et al., acteristics of distance effect in order judg- 2000). ments. Our results demonstrated a strong distance effect (see Figures 4 and 5). Spe- Caveats cifically, accuracy increased and reaction times decreased as a function of distance The biggest challenge to making a strong between two probe stimuli. This implies that conclusion in regards to a specific mecha- the representation of position for adjacent nism of order coding based on the presented items overlap more and might result in more results is the separation of the distance ef- difficult relative position judgments than in fect from the serial position effects. Namely, the case of nonadjacent items (Göbel et al., to be able to identify the correct order of 2011). items, one depends, to a large extent, on the These results closely match observations items being remembered in the first place. in studies of verbal WM reporting strong The task should be easier in the case where distance effect (Angiolillo-Bent, Rips, 1982; the items to be compared are better remem- Buckley, Gillman, 1974; Dehaene et al., 1990; bered. In the case of accuracy, there were no Holyoak, 1977; Moyer, 1973; Proctor, Healy, differences in item recall for positions 1 1987), suggesting that similar mechanisms through 3, so better accuracy for order com- of order coding might be employed for both parison of items 1 and 4 than for items 3 and modalities. The specific pattern of results is 4 cannot be explained by position effects most congruent with magnitude coding of alone. With the reaction time results, how- order information similar to the one proposed ever, the effects are not so clear, as responses for numerical cognition (e.g., Restle, 1970). were fastest when comparing items that Specifically, the order in visual WM could showed reaction time advantage already be represented using a continuous scale present in the item recognition task. It is there- serving as a mental measure of spatial or tem- fore difficult to assess whether the observed poral distance from a common reference point differences in reaction times in order judg- (Brown et al., 2000; Marshuetz, 2005). Ordi- ments can be fully explained by position ef- nal position in such a system is not coded fects or do they reveal additional contribu- explicitly, so adjacent items will have similar tion of distance effects, supporting the mag- representations and their order is more likely nitude-coding hypothesis. to be confused than in the situation of more To provide more robust evidence in sup- widely separated items that have less similar port of the magnitude coding hypothesis representations, are easier to tell apart, and further studies are needed that will either thus will be responded to more accurately validate the independent influence of order and quickly (Göbel et al., 2011; Jahnke, Davis, distance on reaction times or test the hy- Bower, 1989; Marshuetz, 2005). 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SÉRIOVÝ POLOHOVÝ A VZDIALENOSTNÝ EFEKT PRI VIZUÁLNEJ PRACOVNEJ PAMÄTI

B. D o l e n c, J. B o n, G. R e p o v š

Súhrn: Faktory ovplyvňujúce poradie spracovania informácií vo verbálnej pracovnej pamäti (PP) identifikovali a skúmali početné štúdie, zatiaľ čo o udržiavaní poradia vo vizuálnej pracovnej pamäti sa vie len málo. Aby sme lepšie pochopili možné mechanizmy, ktoré reprezentujú poradie vo vizuálnej PP, hodnotili sme rozsah sériového polohového efektu a efektu vzdialenosti položiek pri vizuálnej PP. Testu vizuálnej PP sa zúčastnilo 20 študentov. Ich úlohou bolo kódovať a pamätať si identitu alebo časové poradie štyroch vizuálnych podnetov. Výsledky ukázali, že efekt novosti a vzdialenosti sú v súlade s výsledkami predchádzajúcich štúdií verbálnej PP, nezistil sa však žiaden efekt prvotnosti v presnosti. Vzdialenosť úzko súvisela s novosťou, čo sťažovalo určenie ich samostatného vplyvu na znovupoznávanie poradia. Z výsledkov teda vyplýva, že kódovanie poradia vo vizuálnej PP zahŕňa aj použitie množstva kódov podobných tým, ktoré sa používajú v PP spracúvajúcej čísla a vo verbálnej PP.