Two Techniques for Investigating Perception Without Awareness

Perception & Psychophysics 1985, 38 (3), 296-298 Notes and Comment

Two techniques for investigating perception forced-choice discrimination concerning S, should be without awareness used.

JOHN DUNCAN Forced-Choice Identification MRC Applied Psychology Unit, Cambridge, England One criterion for lack ofawareness is inability to make a forced-choice identification of Sl (Cheesman & Meri kle, 1984; Purcell et al., 1983; others have used inabil This note deals with the logic of recent experiments on ity to identify S.. but not forced-choice: Carr et al., 1982; perception without awareness. In these experiments, a McCauley et al., 1980). Suppose, for example, that S, stimulus is presented in such a way that some forced is always one of four color words, RED, YELLOW, choice discrimination concerning that stimulus is at GREEN, or BLUE. An exposure duration is established chance. Usually this involves use of a backward pattern at which the subject's report of which S, has been mask. Evidence is then sought that, despite chance per presented falls to chance. The experiment searches for formance on the forced-choice discrimination (' 'lack of evidence that S. can nevertheless influence the time taken awareness"), processing of the stimulus is indicated in to name a subsequent color patch. A design of this sort some other aspect of behavior. asks straightforwardly whether two different response I shall use priming experiments as an example. The measures-overt report and priming-can be dissociated masked stimulus S, is immediately followed by a second, intheir sensitivity to exactlythe same stimulus information. clearly visible, stimulus, S2. The question of interest is whether the identity of S, can influence response to S2' Presence-Absence Judgments For example, S, might be a color word, and S2 an ink A second possible discrimination concerning S. is patch whose color the subject is to name as fast as possi forced-choice presence-absence judgment. Presence ble. A Stroop effect (i.e., an effect of congruence or in absence judgments provide an intuitively appealing congruence between S, and S2), occurring even when dis criterion for awareness, since it is tempting to suppose criminations concerning S, were at chance, would be taken that a person who does not even know that a stimulus has as evidence for perception without awareness. Experi been presented can know nothing at all about it. Accord ments of this sort have looked at the effects of various ingly, these judgments have been used in the majority of relationships between S, and S2' using both words and experiments (Balota, 1983; Fowler et al., 1981; Marcel, pictures as stimuli. 1980, 1983; less formally by Allport, 1977; Evett & Hum The evidence on whether such priming effects can be phreys, 1981; Humphreys et al., 1982). found is in fact quite mixed (for positive results see Balota, It is useful to introduce here a simplified version of the 1983; Carr, McCauley, Sperber, & Parmelee, 1982; typical priming experiment. Sl is one oftwo possible let Fowler, Wolford, Slade, & Tassinary, 1981; Marcel, ters, A or B. In the presence-absence task the subject de 1980, 1983; McCauley, Parmelee, Sperber, & Carr, cides whether either letter has been presented. An ex 1980, and the related designs of Allport, 1977; Evett & posure duration is established at which this judgment is Humphreys, 1981; Humphreys, Evett, & Taylor, 1982; at chance. In the priming task S, is followed by a second for negative results and methodological criticisms see stimulus, S2 (also at random a letter A or B), to be named Cheesman & Merikle, 1984; Merikle, 1982; Purcell, as fast as possible. Again, an effect of congruence be Stewart, & Stanovich, 1983). In this note I am concerned tween S, and S2, occurring even when presence-absence not with the results themselves, but with the general de judgments concerning S, are at chance, would be taken sign and interpretation of such experiments. as evidence ofperception without awareness. (For present Fundamentally, the logic is one of dissociation between purposes it is not important whether letter naming can in two response measures. Can priming (or some other be fact be primed in this way. S, could equally well be one havioral index) reflect processing of information when of two color words, and S2 one of two color patches.) forced-choice discrimination does not? With this question It can be seen that, in this experiment, two factors are in mind, I shall consider the question of what should be confounded. The first is the factor of interest-the dis taken as a criterion for lack of awareness, that is, what tinction between two behavioral indices of perception, forced-choice report and priming. The second is the stimu lus information-the information concerning Sl-relevant I thank Lindsay Evett, Tony Marcel, Phil Merikle, and Kit Pleydell to the task. In the presence-absence task there are three Pearce for comments on an earlier draft. The author's mailing address is: MRC Applied Psychology Unit, 15 Chaucer Road, Cambridge, possible stimuli-the mask alone, the mask immediately CB2 2EF, England. preceded by A, and the mask immediately preceded by

B. The subject must discriminate the first stimulus from absence judgments as a criterion of awareness, however, the other two. In the priming task, the important distinc is that the stimulus information on which they depend tion is between the second and third stimuli, mask-plus the distinction between any SI and a blank display-is sim A and mask-plus-B. The important discriminations con ply different information from that of relevance to other cerning 8 1 are different in the two tasks. behavioral indices, such as priming. One way to emphasize the importance of this differ ence is to return to the intuition that a person who does Why Avoid Forced-Choice Identification? not know that a stimulus has been presented can know There is one good reason why many experimenters nothing at all about it. In fact, in the simplified experi avoid forced-choice identification. For many questions ment, it is not at all inconceivable that deciding whether concerning priming, SI must be drawn from a large set a letter had been presented could be harder, not easier, .of possibilities, for example, words of given length (Evett than deciding which letter it was, given that it was present. & Humphreys, 1981; Humphreys et al., 1982; Marcel, Ofthree stimuli-mask, mask-plus-A, mask-plus-B-the 1980). Under these circumstances it is difficult or impos first could easily be the hardest to discriminate from the sible to establish that forced-choice identification is at other two. The absence of any curved line, for example, chance; the chance level may not even be known, or may might be strong evidence against mask-plus-B but of lit be so low as not to be practically measurable. tle use for discriminating mask and mask-plus-A, and so One solution might be to establish, perhaps in separate on. experiments, that whatever awareness criterion is used (It is interesting, with this in mind, to ask why our in either leads to exposure durations similar to those that tuition concerning the primacy of presence-absence judg would have been obtained with forced-choice identifica ments is so strong. I suggest that it is based on our nor tion, or is somewhat conservative in producing slightly mal experience with unmasked stimuli. A letter A shorter durations. For example, the adopted criterion presented on a white card is certainly far more discrimin might be compared to forced-choice identification in a able from a blank card than it is from a similar card with separate experiment with a smaller population of SIS. a letter B. With this sort of stimulus it is indeed hard to Wherever possible, however, it would be best to use imagine that the A-B discrimination could be made when forced-choice identification itself. the A-blank or B-blank discrimination could not. Mask ing, however, may well change the situation.) Summary Of course, the suspicion is that, with the stimuli of a Most experiments on perception without awareness seek typical priming experiment (e.g., 8 1 drawn from a large to show effects of stimulus processing even when some population of possible words), the information distinguish forced-choice discrimination concerning that stimulus is ing the different SIS will be far less discriminable than at chance. Stimulus identification and presence-absence the information distinguishing anyone SI from a blank, judgment are forced-choice discriminations concerning masked display. In fact, the cues used in making presence different aspects of the stimulus, that is, different sets of absence judgments are probably multiple, variable be alternative stimulus states. For presence-absence judg tween subjects, and dependent on training, feedback, and ments the relevant alternatives are a blank display versus so on. As a subject in such a task, one is aware of cues any nonblank stimulus, whereas for identification, the such as flicker, patches of shading, and so on, some of relevant alternatives are the different possible nonblank which indeed discriminate present from absent trials states. (Balota, 1983; Fowler et al., 1981). Especially if The general logic is one of dissociation. The aim is to knowledge of results is given after each trial, one can soon show that forced-choice discrimination can be dissociated learn to use such cues. If it is true in general that these from other indices ofstimulus processing, such as seman cues allow accurate presence-absence judgments while tic priming. Since all stimuli have many attributes, it is telling the subject nothing about which SI has been important to ensure that the forced-choice discrimination presented, then the normal priming design might be seri and the other index of processing reflect processing of ously biased against finding a dissociation between forced the same stimulus attributes, that is, that they reflect dis choice report and priming-the dissociation of major in tinctions between the same sets of alternative stimulus terest. Reducing exposure duration to the point at which states. Only then can one be sure that any dissociation presence-absence judgments reach chance might be reduc observed reflects the difference in response measure, ing it far below a level at which there is any reportable rather than a difference in relevant stimulus information. information about which S. has been seen-the informa tion of relevance to priming. REFERENCES Presence-absence judgments have other well-known difficulties (Merikle, 1982). With barely visible stimuli ALLPORT, D. A. (1977). On knowing the meaning of words we are un it may be hard to avoid a strong bias toward the "absent" able to report: The effects of visual masking. In S. Dornic (Ed.), At judgment, and, as already suggested, results may be quite tention and performance VI (pp. 505-533). Hillsdale, NJ: Erlbaum. BALOTA, D. A. (1983). Automatic semantic activation and episodic dependent on experimental details such as provision of memory encoding. Journal of Verbal Learning & Verbal Behavior, feedback, or motivation of the subject to search for novel 22, 88-104. stimulus cues. Perhaps the most basic defect of presence- CARR, T. H., MCCAULEY, C., SPERBER, R. D., & PARMELEE, C. M. 298 DUNCAN

(1982). Words, pictures and priming: On semantic activation, con In R. S. Nickerson (Ed.), Attention and performance VlI/ (pp. 435 scious identification, and the automaticity of information processing. 457). Hillsdale, NJ: Erlbaum. Journal ofExperimental Psychology: Human Perception & Perfor MARCEL, A. J. (1983). Conscious and unconscious perception: Experi mance, 8, 757-777. ments on visual masking and word recognition. Cognitive Psychol CHEESMAN, J., & MERIKLE, P. M. (1984). Priming with and without ogy, IS, 197-237. awareness. Perception & Psychophysics, 36, 387-395. MCCAULEY, C., PARMELEE, C. M., SPERBER, R. D., & CARR, T. H. EVETT, L. J., & HUMPHREYS, G. W. (1981). The use of abstract (1980). Early extraction of meaning from pictures and its relation to graphemic information in lexical access. Quarterly Journal of Ex conscious identification. Journal ofExperimental Psychology: Human perimental Psychology, 33A, 325-350. Perception & Performance, 6, 265-276. FOWLER, C. A., WOLFORD, G., SLADE, R., & TASSINARY, L. (1981). MERlKLE, P. M. (1982). Unconscious perception revisited. Perception Lexical access with and without awareness. Journal ofExperimental & Psychophysics, 31, 298-301. Psychology: General, 110, 341-362. PuRCELL, D. G., STEWART, A. L., & STANOVICH, K. E. (1983). Another HUMPHREYS, G. W., EVETT, L. J., & TAYLOR, D. E. (1982). Auto look at semantic priming without awareness. Perception & Psy matic phonological priming in visual word recognition. Memory & chophysics, 34, 65-71. Cognition, 10, 576-590. MARCEL, A. J. (1980). Conscious and preconscious recognition of poly (Manuscript received June 19, 1985; semous words: Locating the selective effects of prior verbal context. revision accepted for publication September 4, 1985.)