Size and Shape of the Subliminal Window

The Roots of Perception U.Hentachel, G. Smith, J.G. Draguns (editors) Q Elsevier Science Publishers B. V.(North-Holland), 1986

103

SIZE A N D SHAPE OF THE SUBLIMINAL WINDOW

Donald P. Spence, Lorrie Klein, and Ricardo J. Fernandez UMDNJ-Rutger s Medical School

INTRODUCTION What is the relationship of conscious awareness to information processing? Our subjective impression of a perceptual stimulus is clearly not isomorphic with the total spectrum of stimulation needed to achieve that inpression, but the form and content of unconscious processing is still open to many descriptions. From one point of view, there is a tendency to equate unconscious processing with The Unconscious, the central concept of psychoanalytic theory. In this view, subliminal experiments become a means of exploring different aspects of the dynamic unconscious and of generating an experimental model for the study of Freud's theory of the mind. From another point of view, most clearly expressed by Marcel (1983b), unconscious processing is essentially content-free and differs from conscious processing in the kind and amount of information available. Our conscious impression is neither more nor less in contact with dynamic aspects of our personality, but simply ''an attempt to make sense of a s much data as possible at the most useful level, according to culturally given presuppositions.. ."(Marcel, 1983b, p.250). According to the first view, a subliminal stimulus, because it is out of awareness, is automatically subjected to the processing features of the dynamic unconscious. These features, generally described as the laws of primary process thinking, include such operations as condensation, displacement, and other forms of transformation; thus, to expose a stimulus below awareness is to assume that i t will necessarily be transformed according to primary process laws. Because unconscious thinking is dominated by wishes (in contrast to conscious thinking which is presumed to be logical), a subliminal stimulus is presumed to have privileged access to the more primitive and infantile aspects of the subject's personality. "A subliminal stimulus containing wish-related content first should make contact

D.P. Spence, L. Klein, and R.J. Fernandez

104

with derivatives of the related wish if the wish is currently active in the individual. .The derivatives could be expected to press for expression without the person's awareness.. I' and the appropriate response measures would reveal an increase in psychopathology (Silverman, 1976, p .625). Thus a subliminal stimulus makes direct contact with the more forbidden areas of the subject's personality, and by carefully manipulating stimulus content and the form of the subsequent response measure, it should be possible to test specific propositions about the nature of the dynamic unconscious. Thus the subliminal stimuli "DESTROY MOTHER" and "CANNIBAL EATS PERSON'' appear to intensify pathology in schizophrenics (Silverman, 1976, pp. 626, 629). More ego-syntonic subliminal stimuli are assumed to diminish unconscious conflict and thus diminish pathology; thus ''MOMMY AND I ARE ONE" in seven different studies (as of 1976) apparently reduced pathology when exposed to schizophrenics (Silverman, 1976, p.629). Differences between subliminal and supraliminal presentations come about because of the differential action of the ego's defensive system. A subliminal stimulus triggers an unconscious wish without bringing it into awareness; a s a result, the expected derivatives are not warded off and produce the expected intensification of pathology. The same stimulus, when supraliminal , will necessarily activate the subject's defenses against that wish, and the resulting affect will be sharply attenuated, perhaps even unseen. According to the second view, a subliminal stimulus maintains i t s veridical form; i t is registered essentially intact; and its effective meaning is no different from its meaning in full awareness. Because of the probabilistic nature of the visual system and because brief exposures bring about a significant reduction in input redundancy, it is expected that some degrading of information takes place at subliminal levels. It should be noted, however, that transformations caused by stimulus instability arc largely probabilistic and should be distinguished from the schematic transformations brought about by the laws of the primary process. According to this view, differences between subliminal and supraliminal presentations are a function of what happens when we impose discrete categories on continuous stimuli; the transition can be thought of as a shift from analogue to digital processing. Thus, to make a conscious report about a percept is to give it a location, a content, and where possible, a meaning. Each of these responses imposes a certain kind of categorization on an underlying continuum of information. Thus Marcel writes that "phe-

..

.

Size and Shape o f the Subliminal Window

I05

nomenal experience consists in the imposition of a particular segmentation and structure on what is otherwise unsegmented ( i . e . , non intensional) and the imposition of a particular interpretation on what otherwise consists of multiple interpretations.

..

(198313, p . 243).

The Freudian model, by contrast, takes what might be called a Polaroid view of the visual system which assumes that what is presented to the visual field is veridically registered and necessarily sent on to the higher centers. But it is not at all certain whether a reasonably complex sentence such as "MOMMY AND I ARE ONE" can be veridically registered at subliminal exposures. Not only must separate words be registered in the proper order, but in addition, they must be syntactically combined in a grammatically lawful manner. Consider first the problem of registration. To read a sentence under ordinary conditions, we must scan it in a left-to-right sequence and make successive fixations over the length of the sentence. Fixations must be carefully controlled with respect to duration and interval.

If the sentence is presented out of awareness, there is no chance for systematic scanning. Depending on where fixation happens to fall, we may register the middle words of the sentence, the last words, or perhaps only the white space before the first word. If a sentence normally rcquiring four fixations is flashed only once, there is an inevitable loss of information no matter how fortunate the direction of gaze. Second, there is the matter of hemisphere activation. If we fixate the middle of the sentence, the first half will register in the left visual field and be processed in the right hemisphere. But there is increasing evidence to indicate! (in normal, right-handed subjects) that the right hemisphere is not equipped to handle complicated syntactic processing (see Zaidel, 1978; Levy, 1983). Under these conditions, the first half of the subliminal sentence might be processed a s a collection of separate words. While the second half of the sentence might be processed in the normal fashion, its meaning would obviously be quite different from the meaning of the complete sentence. A third consideration has to do with foveal proccssing. Stimuli which

register in the foveal region of the eye ( 0 to 3O visual angle) are perceived with substantially greater clarity than stimuli which register in the periphery; indeed, the act of reading is designed to maximize foveai scanning of the string of words. We can ask whether peripheral subliminal stimuli would be understood more in terms of overall shape than a s a string of letters ( i . e . , seen as a form rather than a word). Such differences would have obvious implications for what meaning is being registered.

I06

D.P.Spence,L.Klein, and R.J. Fernandez

Thus it would appear as if a subliminal message of more than one word or subtending more than 3O of visual angle might have quite different meanings depending on where in the visual field i t registered and under what degree of fixation control. Peripheral words might be registered with different (less word-like) meanings than foveal words. If the stimulus is centered around the fixation point, only some words may be syntactically processed. Words in the left visual field (right hemisphere) might be processed independently and not syntactically. The resulting consequence of these transformations might appear to be the result of primary process mechanisms, but to invoke such an explanaticn would be less than parsimonious if simpler explanations can be found. The uncertainties surrounding subliminal exposures nay also explain the changing face of the literature. It seems uncommonly difficult to replicate results in this field (see Table 1) and some of the unreliability may stem from the fact that the subliminal stimulus presented by the replicating experimenter is not necessarily the stimulus presented in the original study. If fixation is not controlled, for example, different parts of the message

will register on different parts of the retina at different times, and the effective stimuli might easily vary across experiments. Any experiment using complex stimuli which require some degree of syntactic processing is particularly vulnerable to these variations. Conversely, the chance of successful replication would be substantially improved if' the mechanisms of verbal perception were brought under tighter experimental control. Such controls might often be counter-intuitive. For example, if we are right in arguing that syntactic processing in right-handed subjects is generally impaired in the right hemisphere (left visual field), then it follows that a complex subliminal stimulus must necessarily be presented to the right of the fixation point (stimulating only the right visual field or left hemisphere) and not centered on the screen, as is normally the case, In addition, eye fixation must be carefully controlled. Under these conditions, there would also be critical limits to the length of the message ( i . e , , the size of the visual angle) because only half of the visual field would be available. And finally, if the left hemisphere is critical for syntactic registration, it would be necessary to exclude left-handed subjects because they tend to be unevenly lateralized. From a sample of recent subliminal experiments (all studies published from February 1980 to August 1983 in the JOURNAL OF ABNORMAL PSYCHOLOGY) we compiled the accompanying table (see Table 1 ) . It can be

Size and Shape of the Subliminal Window

I07

Table 1 Perceptual Features of Recent Subliminal Studies

study

Stimulus

Fixation

Lines of Messas

Visual Angle Results (degrees)

* Condon and

no information

MOMMY AND I ARE ONE

?

not available

n.s.

2

Horizontal:6.09'

n.s.

DADDY AND 1 ARE ONE

Allen, 1980

Heilbrun, 1980 frame of blank

BEATING DAD IS OK

* Experiment I

field

* Experiment I1

fixation point

SAME

2

same

n.s.

Experiment I11 fixation point

SAME

2

same

n.s.

*

Ariarn and

frame of blank

Siller, 1982

field

BEATING DAD IS WRONG

MOMMY AND 1 ARE ONE

Vertical: 1.43'

2

Horizontal:9.2'

p= .01

MY TEACHER AND I ARE

(computed from

for main

ONE (Hebrew trans-

authors' data)

effect

lations)

of stimulus

* Haspel and Harris, 1982

* Oliver and Burkham, 1982

frame of blank

BEATING DAD IS OK

field

BEATING DAD IS WRONG

frame of lighted MOMMY AND I ARE ONE screen; Ss told

2

Horizontal:3.9lo

n.6.

Vertical: 1.30'

7

not available

n.s.

MOMMY LOVES ME AS I AM

to "focus on the center of the screen"

Indicates a failure to replicate N.B.

Handedness was not measured i n any experiment. We are also assuming that the stimulus

was always centered in the fixation field although this information was never made explicit.

seen that none of the studies controlled for handedness; that all of the studies apparently centered the subliminal stimulus in the visual field; that only two studies out of seven used a fixation point; and that in five studies the subliminal stimulus subtended a visual angle of more than 3 O , putting parts of the message outside of the foveal area (assuming central fixation). Such an assumption is naturally problematic in all studies using the frame of the blank field to outline the stimulus area; under these condi-

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D.P. Spence, L. Klein, and R.J. Fernandez

tions, it is anyone's guess which parts of the stimulus were being registered. Where the stimulus subtended a large visual angle, particularly when it was presented in two lines of type, w e must assume that multiple fixations were needed to scan the complete message. In many cases, the message was presented more than once (four exposures seems the mode), but without controlled fixations, four exposures will produce just as much of a word salad a s one presentation. Even when fixation was controlled (as in Heilbrun's Experiments I1 and HI), there is still the uncertainty surrounding right hemisphere registration. Assuming that only the right-hand segment is syntactically processed, the meaning of BEATING DAD IS O K , distributed over two lines, is going to be quite different from the meaning intended by the experimenter. And even if all four words were registered, a difference in processing sequence from that intended by the experimenter would obviously result in a difference in meaning. To explore the dimensions of the subliminal window, w e took advan-

tage of the fact that the time needed to decide whether a stimulus is a word or a nonword is significantly shortened when the target word is either accompanied b y , or preceded b y , a related prime ( e . g . , NURSE-DOC* TOR). Meyer et al. (1975) have shown that the recognition of a target word is significantly shortened when it follows the appearance of a supraliminal associate; Marcel and Patterson (1978) and Marcel (1983a) extended the finding to tachistoscopic stimuli; and Crawford (1981) has shown that a priming effect also obtains when the prime is peripheral to the fixation point and therefore slightly out of awareness. We attempted to extend Crawford's procedure to nearliminal and subliminal exposures. In the first two studies reported here, w e presented the prime in one of four positions in the visual field: focal right, focal left, peripheral right, and peripheral left. We expected to find more priming effect in the two focal positions because the stimulus would register with greater clarity at those locations. We also expected that primes in the right visual field would be more effective because they were engaging the left hemisphere. Whatever the outcome, the pattern of results would give us an approximate idea of the shape of the subliminal window. We would then be in a position to present more complex stimuli across the most sensitive part of the window. In Ex-

*

We are indebted to Dr. Hollis Scarborough for f i r s t suggesting t h i s p o s s i b i l i t y .

109

Size and Shape of the Subliminal Window

periment 111, we presented the complex message to only one visual field; in Experiment I V , w e presented the complex message to both fields. Both experiments would allow us to study the interaction of syntactic processing with hemisphere. The subjects in the four following experiments were all members of the Rutgers school community. They had at least a high school education, and the majority had finished college. This was probably thcir first subliminal experiment. They had practically no knowledge of this area of research.

EXPERlMENT I METHOD

Subjects. Eleven Rutgers College undergraduates (3 males, 8 females,aged 18 to 32) participated in the experiment, All subjects were strongly right-handed

with scores of 15 or above on the Edinburgh Inventory (Oldfield, 1971). The Edinburgh Inventory is a widely used test of handedness which consists of 12 items each related to a specific activity ( e . g . , which hand do you use to deal playing cards?). Each item is scored on n five- point scale from always right (+2) to always left ( - 2 ) ;

the twelve items are sumrncd

and the highcr the score, the more right-handed the subject. It goes without saying that scorcs can range from 24 to - 2 4 . A score of 9 to 24 is usually taken as the criterion for righthandedness

.

Stimuli. The priming stimuli were presented at two speeds

-

135 and 30 msec.

One hundred and fourteen target words were presented in each condition. Each list was composed of 96 real words plus 18 pronounceable nonwords. The real words ranged in length from 3 to 7 letters and in frequency from 1 to 1599 occurrences per million words (ICu6era and Francis, 1967). Each

real word was preceded by one of three classes of primes: semantically related (e.g. , STORY-BOOK) ; semantically unrelated (e.g.

, WINDOW-PEEL) ;

and pronounceable nonsense (e.g., EMPOD-LOOK) , Half of the semantically related primes on each list were abstract nouns or adjectives ( c . g . , REASON) which were all below 4 . 7 3 on the norms published by Toglia and Battig (1978), and half were concrete nouns or adjectives ( e . g . , LION), all above 5.15. Primes ranged in length from 4 to 6 letters. If hemisphere ac-

D.P. Spence, L. Klein, and R.J. Fernandez

110

tivation made a difference, w e would expect to see the left hemisphere particularly sensitive to abstract primes (see Day, 1977; Ellis and Shepherd, 1974).

Each priming stimulus was presented in one of four positions in the subject's visual field. Focal right and left displaced .5 to 2.6O of visual angle and peripheral right and left displaced from 4.7 to 7 O of visual angle on either side of the fixation point. For any given stimulus position ( e . g . , focal right), 24 pairs of words were divided equally between the two types of primes (abstract and concrete) and the three types of semantic link (related, unrelated, and nonsense). Each of the six cells contained four pairs of words. Target words were balanced for length and frequency across semantic link. Position and type of prime was systematically randomized over the list. Nonword targets were presented intermittently and neve r appeared more than twice in a row. Eye movements were controlled by the use of a constant fixation point, by a chin rest which stabilized the subject's head, and by the use of a vertical target word which required the subject to center his gaze on the fixation point. Deviations from midfield would significantly increase reaction times to the target word and thus diminish the expected priming effect (Note 1). Apparatus. The stimuli were presented by an Apple I1 Plus micro-computer. Rate of presentation was controlled by the experimenter by means of a telegraph key patched into the Apple 110 connector. Reaction times were measured by an assembly language subroutine which measured the interval from the appearance of a target word to the keypress by the subject, using a timing * board obtained from Mountain Computer, Inc. Timing of the subliminal stimulus, the onset-offset interval, and random readings of the internal clock were checked by a millisecond timer patched into the Apple 1 / 0 connector. Times and keypress locations were stored by the same program that presented the stimuli. Visual angle was controlled by fixing the subject's chin in a rest 25.6 inches from the monitor screen. Each prime was exposed (at either 135 or 30 msec., depending on condition ) by pressing the telegraph key. A white mask in the same plane as the fixation point immediately followed the prime and remained visible for either 80 or 185 msec. (duration of prime plus mask always added to a con-

*

We are indebted to Dr. Hollis Scarborough for first suggesting t h i s possibility.

Size and Shape of the Subliminal Window

111

stant). It was followed immediately by the target word which appeared vertically with its first letter displacing the fixation point. The target word remained visible until the subject pressed one of the two response keys. Illumination levels were set at 2 . 4 footlamberts for the blank screen of the Apple monitor; 2.45 footlamberts for the prime and target words; and 3.0 footlamberts for the horizontal white mask. The room illumination was set at .20 footlamberts. All four experiments used the same illumination levels. Procedure. Subject was seated in front of the monitor, chin in the chin r e s t , and his index fingers placed on the left and right response keys ( A and L on the Apple keyboard). Each subject was asked to focus on the s t a r which appeared in the middle of the screen. He was told that after a warning click he would see a word appear vertically in the center of the screen and had to decide, as quickly a s possible, whether it was a word o r a nonword. H e was to press the left key if it was a word and the right key if it was a nonword. Speed and accuracy were stressed. After about every 25 words, the subject was given a short rest. Fifteen practice words pre-

ceded the main list. The slow condition always came first. After both lists had been presented, recognition was tested by repeating the first half of each list with slightly different instructions. The subject was told to focus on the s t a r , a s before, and to watch for a word which would appear very quickly before the vertical word. On each expos u r e , he was to report location (left or right, near or far) and content where possible. RESULTS

Each subject’s record was screened first for keypress errors and the average reaction time (RT) in the corresponding cell of four words was adjueted accordingly. All averages were rounded to the nearest millisecond and entered into a four-way analysis of variance with 24 repeated measures. The four factors were: Semantic Link (related, unrelated, control) ; Prime Concreteness (abstract, concrete) ; Visual Field (right, left) ; and Offset (peripheral, focal). Analyses were carried out separately for each exposure speed. 135 msec. Effect of Semantic Link was significant: F=5.72, p e . 0 2 5 ,

2 / 2 0 d.f.

Target words preceded by associates were recognized at an average RT of

112

D.P.Spence, L. Klein, and R.J. Fernandez

626 msec. ; targets preceded by nonassociates were recognized at an aver-

age of 677 msec.; and targets preceded by nonsense words (the no-meaning, o r control condition) were recognized at an average RT of 667 msec. (see Figure 1). The priming hypothesis is supported: if there is a semantic link between prime and target word, it appears to facilitate its recognition; i f there is no semantic link, the prime appears to delay recognition. Average facilitation effect across all words (control - associates) is 4 1 msec. ; average inhibition effect (nonassociate - control) is 10 msec. The pattern of RTs suggests that it is the meaning of the prime and not i t s membership in the family of word-like shapes that is responsible for the facilitation effect. To further clarify the role of meaning, we repeated the analysis with the nonsense primes excluded. Effect of Semantic Link (associates vs. nonassociates) remained significant (F=7.96, p c .025, 1 / 1 0 d.f.) which indicates that even when both primes are words, it is the semantic link to the target word which facilitates recognition. In a final analysis, we compared nonassociate with control and found no main effect (F= .58, p > . 4 ) ; in other words, a meaningful prime will not lower RT if there is no semantic link between prime and target. This finding makes it clear that more than a word-like shape is being processed: some degree of meaning is also being extracted and having an effect on the subsequent target word. Semantic Link interacted

significantly

with

Visual

Field:

F=5.83,

pc.025, 2 / 2 0 d.f. (see Figure 1). Priming was more effective when the associate was presented in the right visual field (which actiirates the left, or language hemisphere). Average RTR for associates, nonassociates , and controls in the right visual field were 578, 653, and 648 msec., respectively, giving a facilitation effect of 70 msec. and an inhibition effect of 5 msec. The corresponding values for the left visual field were 674, 7 0 4 , and 686 msec., respectively, giving a facilitation effect of 1 2 msec. and an inhibition effect of 18 msec. Semantic Link interacted significantly with Prime Concreteness : F= 3.88, p c . 0 5 , 2 / 2 0 d.f. (see Figure 1). Priming was more effective with concrete than with abstract stimuli (e.g., LION vs. REASON). Average FtTs for associates, nonassociates, and controls for concrete primes were 631, 709, and 710 msec., respectively, giving a facilitation effect of 79 msec. and an inhibition effect of -1 msec. The corresponding values for abstract primes were 621, 648, and 624 msec., respectively, giving a facilitation effect of 3 msec. and an inhibition effect of 24 rnsec.

Size and Shape of the Subliminal Window

1 I3 -1100

ABSTRACT P R I M E S

L

RELATED UNRELATED NONSENSE

135msec R T l m s e c ) 900

800

700

600

500

CONCRETE

i I

'H

LEFT VISUAL FIELD

RIGHT VISUAL FIELD

(RIGHT HEMISPHERE)

(LEFT HEMISPHERE)

NONWOR

500

1100

PRIMES

'-7 -. RELATED 0 UNRELATED NONSENSE

R T l m s e c l 900

no0

700

600

500

ioo PERIPH

FOCAL

LEFT VISUAL FIELD IRIGHT HEMISPHERE 1

Figure 1

FOCAL

PERIPH

NONWORO

RIGHT V I S U A L FIELD ILEFT HEMISPHERE)

Faperiment I. Reaction time for correct recognition of the target word when it was preceded by related, unrelated, or nonsense stimulus as a function of visual field and p r i m concreteness.

D.P.Spence, L. Klein, and R.J. Fernandez

I14

There was a significant triple interaction between Semantic Link, Offs e t , and Prime Concreteness: F=5.29, p c . 0 2 5 ,

2/20 d.f.

For concrete

primes, facilitation effects were roughly equal in both focal and peripheral fields, whereas inhibition effects appeared only in the focal field. For abstract primes, facilitation effects appeared only in the peripheral field, whereas inhibition effects were roughly equal in both fields. Finally, there was a significant four-way interaction between Semantic Link, Offset, Prime Concreteness, and Visual Field: F=6.49, p c -01, 2 / 2 0 d.f. The strongest facilitation effect occurred with concrete right focal field ( 1 4 2 msec.) ; the weakest effect occurred primes in the right focal field (-60 msec.) (see Figure 1). inhibition effect occurred with abstract primes in the right

primes in the with abstract The strongest focal and left

peripheral fields (100 msec. ) ; the weakest inhibition effect occurred with concrete primes in the left peripheral field (-65 msec.). The fact that we found no significant interaction between Offset and Semantic Link indicates that the priming effect is just as strong when the prime was presented in the peripheral field (displacing a visual angle of 7O) a s when it was presented to the focal field of . 5 to 2 . 6 O . It would appear a s i f 135 msec. were sufficient time to allow a peripheral sti-

4 . 7 to

mulus to register as a meaningful icon and to be processed for i t s semantic and imagistic information. At the same time, the four-way interaction makes it clear that a subliminal effect will be maximized by presenting a concrete stimulus in the focal right visual field subtending a visual angle of no more than 3O. Such a stimulus would seem to activate both the semantic and imagistic coding systems and is processed by the left hemisphere where these codes are presumably more systematically represented. The fact that we found no interaction between prime concreteness and visual field indicates that the left hemisphere is no more sensitive to concrete than to abstract primes. Unlike Ellis and Shepherd (1974) or Day (1977), we did not find a greater visual field asymmetry for abstract than for concrete stimuli. 30 msec. To measure the effect of the subliminal prime when it was flashed a t 30 msec., we carried out a second four-factor ANOVA with repeated measures. (One subject was eliminated because he made too many errors. ) The main effect of Semantic Link was not significant. There was a marginal interaction of Semantic Link with Prime Concreteness (F=2.93, p e . 0 8 , 2 / 18 d.f.1 and a signiricant four-way interaction of Semantic Link X Prime Concreteness X Visual Field X Displacement (F=6.56, p c .01, 2/18 d.f.1.

Size and Shape of the Subliminal Window

115

Recognition of prime varied significantly with speed, visual field, and offset. In the slow condition, correct recognition averaged 388, ranging from 25 to 51%. In the tast condition, the average was 25% correct, ranging from 9 to 42%. Recognition of right field primes was superior to left field primes, and recognition of focal primes was superior to peripheral primes. Each of the main effects

-

speed, position, and offset

-

was significant;

the respective Fs are 66.28, 11.79, and 415.48. There were no significant interactions. Of particular interest is the fact that 6 Ss in the slow condition re-

cognized no words correctly when they appeared in either the right or left peripheral fields; for the fast condition, the number increased to 11 (the total sample). On the average, recognition was from five to ten times more effective when the prime was focal than when it was peripheral, a difference that accords well with our knowledge of retinal architecture. Yet despite the clear effect of offset on recognition, we failed to find a similar tendency when we looked at changes in RT. In the slow condition, peripheral primes seemed fully a s effective as focal primes, and we found no interaction between offset and semantic link. These two findings taken together can be seen as evidence for preconscious processing. Peripheral primes appear to influence the recognition of related target words even when the prime cannot be consciously recognized. Errors. Errors in response to the target word ranged from 0 to 7 in the 135 msec. condition and from 0 to 4 in the 30 msec. condition. In the former, significantly more errors were caused by peripheral primes than by focal primes (F=11.01, p e . 0 1 , 1/10 d . f . ) ,

and more errors were caused by

primes in the left visual field than by primes in the right visual field (F=

5.26, p e . 0 5 , 1/10 d.f.1.

Neither of these effects were sustained in the

fast condition. DISC USSl ON Primes presented for 135 msec. produced a significantly shorter rcsponse to a semantically related target word. We can assume that the expo-

sure of the prime activated a network of associates which somehow facilitated the S's lexical decision. The facilitation effect was particularly pronounced in the right visual field (left hemisphere) and appeared more clearly with concrete primes. We might assume that the association network

116

D.P. Spence, L. Klein, and R.J. Fernandez

is more faithfully represented in the left hemisphere : thus hypotheses based on different kinds of semantic links and different degrees of association strength (the assumptions underlying the pairing of the prime and target words) would apply with more force to stimuli presented to the right visual field. Much less clear are the findings form the fast condition. At 30 msec., the p r i m failed to produce a significant savings in S's lexical decision, although we did see a slight advantage of concrete over abstract primes. Either a brief presentation was insufficient to activate the association network, or the level of prime-target association strength was not sufficiently high to activate an enabling hypothesis. Some evidence contributing to this possibility appears from a comparison of the association strength of concrete primes and targets in the slow and fast conditions. In the former, the average association strength is Z56

-

that is, 256 subjects out of a

sample of 1000 chose thc target word as their first response to the prime. In the latter, the average association strength is 125. A s a result, we would expect that many concrete primes in the fast condition would activate a hypothesis which would not match the target word, thus leading to a delayed instead of a quickened RT. Thus the difference in activation may be less a function of prime exposure than a consequence of a difference in association strength. The next experiment controlled for association strength. In addition, two other changes were made. Instead of concrete and abstract primes, we chose to use primes with high levels of imagery on the assumption that this variable may be more directly related to hemisphere asymmetries. And because of the possibility that the offset-onset interval in the fast condition was too long and as a result suppressed the priming effect, we shortened the interval to a standard length. EXPERIMEN J I / METHOD

Subjects. Twelve members of the Rutgers Mcdical School community participated in the experiment. There were 6 males and 6 females, ages ranging from

17 to 37. All were strongly right-handed with scores of 16 or above on the Edinburgh Inventory. Stimuli. The stimuli were presented in two lists of 95 words each: 80 target words plus 15 pronounceable nonwords. The target words ranged in length

Size and Shape of the Subliminal Window

I17

from 3 to 6 letters and in frequency from 1 to 1207 occurrences per million words. They were all nouns. Each target word was preceded by either an associated word or a pronounceable nonsense word. Two levels of association were used, as indicated by word association norms (Palermo and Jenkins, 1954). The targets were either high associates of the prime (having a frequency between 80 and 706 out cjf 1000 subjects at college level) or low associates (frequency between 6 and 18). All of the primes were high imagery nouns, with a mean score of 5.86 and a range from 5.22 to 6.38 (Toglia and Battig, 1978). Each prime appeared twice (but never in succession), once with a high associate target and once with a low associate target. Control targets, matched to the associated targets by usage frequency and word length,

were preceded by nonsense primes.

Primes

ranged in length from 4 to 6 letters. The primes were positioned in the visual field as in Experiment 1. In this experiment, however, the primes were presented at 7Omsee. on the first list and at 30 msec. on the second list. The offset-onset interval was always fixed at 80 msec. For any given stimulus position (e.g., focal right), the 80 prime-target pairs were equally divided between the four types of semantic link (high and low associates and matched controls). Each of the 16 cells contained 5 word pairs. Target words were balanced for length, frequency, and imagery across semantic link and position. Position and type of prime were systematically randomized over the list. Nonword targets were presented intermittently and never appeared twice or more in a row. The two word lists were given in opposite orders for half the subjects. Procedure. Same as in Experiment I except in recognition testing. In this part of Experiment 11, both complete lists were given. The subject was told that occasionally the question l'WORD?'f would appear in the upper left-hand corner of the screen after he had made a word vs. nonword decision. When this occurred, the subject was to report the content and location (left or right, near or far) of the word (if he saw one) that flashed by prior to the target word. RESULTS

Each subject's record was screened for keypress errors and the cell averages adjusted accordingly. For each condition, we reduced the data by means of a four-factor analysis of variance with repeated measures.

118

D.P. Spence, L. Klein, and R.J. Fernandez 70 msec.

Effect of Semantic Link was highly significant: F=45.0, p<.OOl, 1/11 d.f. Target words preceded by associates were recognized at an average RT of 707 msec., whereas target words preceded by nonsense primes were recognized with an average RT of 781 msec.. yielding a facilitation effect of 74 msec. (see Figure 2 ) . There was no significant interaction between Semantic Link and level of association. There was, however, a main effect of association level (F=8.60, pc.025, 1/11 d.f.1; targets preceded by high associate primes (and paired nonsense words) were recognized faster (719 msec.) than targets preceded by low associate primes and their pairs (769 msec.). Because the crucial difference lies in the link between related prime and target word (the nonsense primes, after all, are uniformly unrelated), this finding would seem to support the hypothesis. To clarify the meaning of this finding, we repeated the analysis using only the nonsense primes. The difference between high and low groups was not significant (F=2.71). It would seem that when the target word is preceded by a prime which is highly related in meaning, its recognition is significantly improved, suggesting that what might be called the semantic demand characteristics of the prime have an influence on recognition of the target word. Semantic Link interacted significantly with Offset: F = 9.34, p < ,025, 1/11 d.f. When the primes were presented in either right or left focal field, the facilitation effect was 114 msec.; when the primes were presented in either peripheral field, the facilitation effect decreased to 34 msec. Finally, there was a significant interaction between Semantic Link,

Level of Association, Visual Field, and Offset: F=15.22, p < .005, 1/11 d.f. The shortest RT occurred in the peripheral right visual field with highstrength associates; the longest RT occurred in the focal right visual field with nonsense primes. Recognition. Correct identification of the nearliminal primes ranged from 4 to 22 out of a possible 4 0 ; it was significantly influenced b y Offset and Visual Field. Main effect of Offset was highly significant (F=75.45, p < ,001, 1/11 d.f.1 with focal primes recognized much more often than peripheral primes. Main effect of Field was significant (F=41.59, p < .001, 1/11 d.f.1 with primes in the right visual field recognized more often; and the interaction of Offset by Field was significant, with proportionately more primes recognized in the focal right than in the peripheral right visual field (F=5.62, ~ 4 . 0 5 , 1/11 d.f.1. The focal primes would seem to be nearliminal, whereas

Size and Shape of the Subliminal Window

119

T I2Oo 0

t

ASSOCIATE NONSENSE

RT(msec)SOo

800

700

600

600 PtRlPH

FOCAL

FOCAL

PERIPH

PfRlPH

FOCAL

FOCAL

PtRlPH

NONWORO

LEFT VISUAL FIELD LEFT VISUAL FIELD RIGHT VISUAL FIELD RIGHT VISUAL FIELD

HIGH ASSOCIATION

LOW

ASSOCIATION

1l2O0

0 ASSOCIATE

PtRlPH

FOCA1

FOCAl

PERIPH

PERIPH

FOCAL

FOCAL

PERIPH

NONWORO

LEFT VISUAL FIELD LEFT VISUAL FIELD RIGHT VISUAL FIELD RIGHT VISUAL FIELD HIGH ASSOCIATION

Figure 2.

LOW

ASSOCIATION

Experiment 11. Reaction time for correct recognition of the target word when it was preceded by h i g h imagery associates and nonsense words as a function of exposure speed, visual f i e l d , and level of association between prime and target.

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D.P.Spence. L.Klein, and R.J. Fernandez

the peripheral primes are much more subliminal, and this difference in awareness was partly reflected in target recognition, for as we have just seen, targets preceded by focal primes were identiried faster than targets preceded by peripheral primes. But because there was a main effect for Semantic Link, it follows that awareness of the prime is not a necessary condition for facilitation. Awareness of position was much better than correct identification. Number of correct lateral placements (right or left) ranged from 29 to 40, and number of correct offset placements (near or far) ranged from 23 to 40.

To get a better understanding of the extent to which awareness might have contributed to the facilitation effect, we divided the sample into two groups according to the number of primes correctly recognized and repeated the initial four-factor analysis. Interaction of Semantic Link with awareness was not significant, indicating that the more-aware subjects were not more responsive to the nearliminal prime than the less-aware subjects. Errors, Keypress errors ranged from 0 to 6. A four-factor a r d y s i s of variance showed a main effect for Semantic Link (F=5.20, p c .05, 1/11 d.f.1 with more errors following nonsense primes than target associates; a Visual Field X Semantic Link interaction, with proportionately more errors following the nonsense primes in the right visual field than in the left visual field: F=6.49, p c .05, 1/11 d.f.; and a significant interaction between Visual Field, Level of Association, and Semantic Link: F=5.36, p c . 0 5 , 1/11 d.f. No subject made any errors on the 10 target words preceded by high associate primes, whereas the greatest number of errors (50% of the subjects) were made on target words preceded by nonsense primes. 30 msec. Effect of Semantic Link was highly significant: F=35.05, p c .001, 1/11 d.f. Target words preceded by associates were recognized at an average RT of 666 msec. ; target words preceded by nonsense primes were recognized at an average R T of 742 msec., yielding a facilitation effect of 76 msec. Once again, degree of association did not interact with Level of Association, but as before, there was a main effect of Association Level (F= 8 . 7 , p c . 0 5 , 1/11 d.f.1 which stemmed largely from the related associates. When the analysis was repeated with only the nonsense primes, the effect of level disappeared (F=.03), an indication that level of semantic link plays an important role in the facilitation effect.

Size and Shape of the Subliminal Window

121

Neither Visual Field X Semantic Link nor Offset X Semantic Link interaction was significant, indicating that the associate prime was equally effective in all four locations. There was a near-significant interaction between Semantic Link, Level of Association, Visual Field, and Offset: F=4.74, p c .06, 1/11 d.f. The largest facilitation effect occurs in the right focal visual field with highstrength primes; the lowest effect occurs in the left focal visual field with low-strength primes. To look more carefully at the effect of peripheral primes, we repeated the analysis but excluded the focal stimuli. Effect of Semantic Link was still significant (F=9.52, p c .025, 1/11 d . f . ) with target words preceded by associates recognized with an average RT of 652 msec. and target words preceded by nonsense primes recognized with an average RT of 722 msec. (facilitation effect = 70 msec., roughly the same difference as was found using all the data). Semantic Link did not interact with visual field (F= .12), an indication that both right and left peripheral primes are equally effective in facilitating the response to related target words. These data would suggest that high imagery stimuli can be registered in the more peripheral parts of both visual fields (visual angles from 4 . 7 to 7 O ) and that meaning can be extracted by both right and left hemispheres. Recognition. Correct identification of primes ranged from 7 to 2 1 out of a possible 40; once again, i t was significantly influenced by offset and visual field. Main effect of Offset was highly significant (F442.55, p c .001, 1/11 d.f.1

with focal primes recognized much more often (%=3.25 out of a possible 20) than peripheral primes (Z=.29). Main effect of Field was significant (F= 44.45, p c .001, 1/11 d.f.) with primes in the right visual field recognized more often than primes in the left; and the interaction of Offset by Field

was significant, with proportionately more primes recognized in the focal right than in the peripheral right visual field (F=70.40, p c .001,

1/11

d.f.). Awareness of lateral position (right or left ) ranged from 29 to 40, and awareness of offset (near or far) ranged from 28 to 39. To further understand the role of awareness, we again divided the subjects into two groups according to correct recognition and repeated the analysis. There was no Awareness X Semantic Link interaction. Errors. Keypress errors ranged from 0 to 3. A four-factor analysis of variance revealed no main effects and no signiricant interaction.

122

D.P. Spence, L. Klein, and R.J. Fernandez DISC USSl 0 N

Target words preceded by semantically related primes were identified faster than equivalent words preceded by pronounceable nonsense words. The facilitation effect occurred at both 70 and 30 msec. and in both right and left visual fields. Degree of offset affected the facilitation effect in the slow condition but was (surprisingly) not a factor in the fast condition. At the faster speed, i t would seem as i f a single-word stimulus registers with equal effectiveness in all four regions of the visual field. Conscious awareness of the semantically related prime did not always parallel the pattern of target word activation, which suggests that awareness may be neither a necessary nor a sufficient condition for the stimulus to affect reaction time. The disparity is particularly striking with respect to the peripheral primes in the 30 msec. condition. Whereas they were recognized significantly less often than the focal primes, their influence on recognition of the target word was not significantly reduced. Even though not in conscious awareness, it would seem as if the peripheral primes triggered an enabling hypothesis which, because it matched the target word, allowed the subject to respond with a faster discrimination, We tentatively hypothesize that even when the stimulus registers outside the foveal area, the icon is maintained long enough to allow for some kind of information transfer. We are now in a position to explore the effects of a complex subliminal message. We have learned from Experiment I1 that the meaning of simple words can be registered even if they are presented as far as 4 . 7 to T o to the left or right of the fixation point. I t now remains to be seen whether a sentence can be syntactically processed when exposed to the same part of the retina. For this experiment, we chose the stimuli llPlense Press Left/ Right" and "DO Not Press LeftlRight .It The expected response to target words is once again a left keypress. If the complete stimulus is processed, we would expect to see slower reaction times to the target word when the stimuli were "Please Press Right" and "DO Not Press Left," and faster reaction times when the stimuli were !'Please Press LeftT1and "DO Not Press Right . I 1 If "Please" and "Do Not" are called Commands and "Left"/"Right" are called Locations, we would expect to see an interaction between Command and Location. On the other hand, if only single words were processed, (as might be the case. for example, when only the right hemisphere is activated), then we might see a main effect for Location and perhaps a main effect for Command. A main effect for Location would pre-

Size ond Shope of the fiblimiwl Window

123

dict that the words "Left" or %ight" would influence reaction time without regard to the earlier part of the sentence; in other words, Location was not modified by Command. A main effect for Command would predict that the words "Please" and "DO Not" would be obeyed without regard to Location. Suppose single words were processed by one hemisphere and the complete sentence in the other. Under those conditions, we might expect to find a triple interaction between Command, Location, and Visual Field.

EXPERIMENT 111 METHOD

Subjects. Ten members of the Rutgers Medical School community participated in the experiment. There were 3 males and 7 females, ages ranging from 16 to 37. All Ss were right-handed with scores of 13 or above on the Edinburgh Inventory. Stimuli Two lists of 95 target words were presented: 80 real words plus 15

.

pronounceable nonwords (the lists were identical to those used in Experiment 11). Half the Ss received List 1 first. The subliminal clue was presented at 30 msec. and appeared in either the right or left visual field; it commanded the subject to "Please Press" or "DO Not Press" and it referred to either of two locations: ttLeft't or 1Right.77The eight possible combinations of two visual fields, two verbs (commands), and two locations were distributed over the 80 target words, yielding 10 words in each cell; cells were matched for word frequency and word length. Nonwords were distributed randomly throughout the list and were preceded by a nonsense prime exposed for 30 msec. in either right or left peripheral field. Offset-onset interval was increased to 230 msec. to allow for syntactic processing of the clue. Procedure. Same as Experiment I1 except for recognition testing; the new version is described below. RESULTS

All lexical choices were inspected first for accuracy; instances of incorrect keypress were deleted; and from the remaining RTs, eight sets of

D.P.Spence, L.Klein, and R.J. Fernundez

124

averages were computed for each subject for each trial. A four-factor analysis of variance was used to reduce the data: the factors are Trial, Command, Visual Field, and Location. Mean RTs are shown in Figure 3 averaged across both trials (the main effect for trials was significant - RTs decrease signiticantly over time, F=7.57, p c ,025, 1/9 d.f. - but there were no significant interactions between Trial and any other variables). RT I msec)

t

1400

00 NOT PRESS

PLEASE PRESS

LEFT VISUAL FIELD (RIGHT HEMIS.) Figure 3.

PLEASE PRESS

00 NOT PRESS

RIGHT VISUAL FIELD (LEFT HEMIS.)

Experiment 111. Reaction time for correct recognition of the target word as a function of visual field, Command (PLEASE PRESS

VS.

Do NOT PRESS), and key

location (Left va.Right).

Main effect for Location was highly significant (F=7.57, p c . 0 2 5 , 1 / 9 d.f.). This finding indicates that RTs to target words preceded by the word trRight17. regardless of context or visual field, were significantly longer (z=863 msec.) than RTs to target words preceded by the word TTLefttq (z=773 msec.) There was a nonsignificant interaction between Location and Visual Field, indicating that the clues TrRightvfand "Lefttt were equally effective in either visual field, despite the fact that in half the trials, they were displaced to the far right of the screen (see Figure 3 ) . Main effect for Command was significant (F=10.64, p c .01, 1 / 9 d . f . ) ; the command "Do Not Press'! resulted (somewhat paradoxically) in significantly shorter RTs than the command "Please Press." I t will be seen from

.

125

Size and Shape of the Subliminal Window

Figure 3 that this difference stems largely from the findings for the right visual field. A significant interaction between Command and Visual Field (F=20.60, p c .005, 1 / 9 d.f.1 supports this observation. Of most relevance to the main hypothesis is the significant interaction between Command, Location, and Visual Field (F=5.33, p < . 0 5 , 1/9 d.f.1 which suggests that Command modified Location more in one visual field than in the other. To further explore this finding, we carried out separate analyses for the two visual fields. When the subliminal clue was presented to the right visual field (left hemisphere), there was a main effect for Command (17.85, p c .002, 1 / 9 d.f.1,

a main effect for Location (F=6.66,

p c .05, 1 / 9 d . f . ) , and a significant Command X Location interaction (F= 6.66, p < .05, 1 / 9 d . f . ) , suggesting that some kind of syntactic processing

is taking place and that Command is modifying Location. As can be seen from Figure 3 , the presence of "DO Not" in the right visual field substantially reduces the RT to "Right." On the other hand, when the clue was presented to the left visual field (right hemisphere), there is only a main effect for Location (F=16.94, p c .002, 1/9 d.f.) and no other main effects or interactions, suggesting that a more primitive kind of processing may be taking place and that only the words "Left" and "Right" were influencing the response to the target word. Figure 3 makes clear that the difference between "Right" and "Left" is essentially the same whether preceded by "Please Press" or "DO Not Press." Although it might be argued that the changes in Command did not register in the peripheral left visual field, evidence from the first two experiments would argue against such an assumption. Recognition. After the two lists had been presented, we sampled awareness of the subliminal clue by presenting 24 target words from one of the previous lists, measuring RT to the target word in the standard manner, and also asking, after each lexical decision, whether anything had been seen to "flash by" before the target word appeared and what and where it was. Twenty-one priming clues were presented, distributed over the eight possible combinations. A complete clue was never seen, and the number of partial clues recognized by any subject ranged from 0 to 8 out of a possible 21. Partial awareness of the clues in the right visual field was greater than awareness of clues in the left visual field; eight Ss were able to identify parts of one or more clues in t h e former as compared to only one

S making partial identification of clues in the latter ( p c .05, two-tailed

126

D.P. Spence. L. Klein, and R.J. Fernandez

Wilcoxon test). Within each visual field, correct recognition of specific clue parts was averaged over all Ss and the scores corrected for frequency of appearance. The percent recognition scores are shown in table 2 . The first Table 2 Correct Recognition of Clue Parts

Experiment 111 L e f t Visual F i e l d

Right Visual F i e l d

W NOTlPLEASE PRESS LEFT/ RIGHT % Correct

3

Subjects (N)

1

0

0

0

0

DO NOTlPLEASE

10

50

5

8

PRESS LEFTlRIGHT

0

0

0

Experiment IV

PRESS

/

AVOID

LEFT

I

RIGHT

More V i s i b l e % Correct

1

7

28

14

Subjects (N)

1

1

4

2

Trial

1

Less V i s i b l e % Correct

0

Subjects (N)

DO NOT

/ PLEASE

2

8

5

1

4

3

PRESS

YOUR LEFT

/

HAND

RIGHT

Spaced % Correct

0

0

Subjects (N)

2.5

0

0

0

0

1 Trial

2

Crowded % Correct

Subjects (N)

0

0

6.2

0

0

0

0

4

word or words in each field are much better identified than subsequent words, and there is a tendency for accuracy to decrease in a left-to-right manner. Number of S s contributing to each score are shown in the second line of Table 2 ; recognition is confined to the first word or words in each clue with "Please" slightly more visible than "Do Not . I q

Size and Shape of the Subliminal Window

127

Errors. Errors per subject ranged from 1 to 7 out of 80 words on the first trial and from 0 to 3 on the second. A four-factor analysis of variance showed a main effect for Trial (more errors in the first

-

F=17.19, pc.002,

1/9 d.f.1; a significant interaction between Trial and Location (more errors following "RightT1 than llLeft'l in Trial 1 but not in Trial 2 - F=5.19, p c . 0 5 , 1/9 d.f.1; and a significant interaction between Command, Location, and Visual Field (F=7.11, p c . 0 3 , 1/9 d . f . ) . On Trial l, where the majority of the errors occurred, the greatest number were made following "Please Press Right" in the right visual field. Since an error results from pressing the right-hand key, the presence of crrors suggests that the subject was responding to the clue and (as instructed) was pressing the right-hand key. This finding would also seem to support the hypothesis that full syntactic processing was taking place in the left hemisphere. On the other hand, the smallest number of errors (0) in Trial 1 followed the clue "DO Not Press Left" in the left visual field. If the full sentence were parsed, it would prompt the subject to press the right-hand key, i.e., to make an error. Because no errors appeared, we can draw the tentative conclusion that syntactic processing did not take place and that the subject responded only to the word "Left" (and perhaps "Press"). DISCUSSION

The results of Experiment I11 make it clear that where the prompting stimulus appears in the visual field makes a critical difference to its interpretation. If it falls in the right visual field, it will more likely be syntactically processed than i f it falls in the left. This finding has obvious implications for those subliminal studies (see Table 1) which fail to provide a central fixation point for the subject. If fixation is constrained by only the outlines of the blank field, what mcssage is syntactically processed will depend on where fixation happens to fall. Table 1 also makes it clear that no experiment has presented the critical stimulus to the right of the fixation point. Only in this way would the total message be processed b y the left hemisphere. The findings of Experiment 111 make this oversight all the more critical because they suggest that, to date, no study has properly tested the impact of a complex subliminal mcssage,

Our findings would suggest that when the subliminal stimulus is centered around a fixation point, the words to the right of center (registered

128

D.P.Spence, L.Klein, and R.J. Fernandez

by the left hemisphere) would be syntactically processed whereas the words to the left of center (right hemisphere) might register in a more primitive manner, not necessarily incorporated in the total stimulus. In an effort to explore these possibilities, we attempted to influence lexical choice with a message that spanned both halves of the visual field. If both hemispheres contribute equally to message processing, we should expect to see an interaction between Command ("Please PressTt vs "DO Not Press") and Location ("Left" vs. "Right"). If stimuli to the left of center are not syntactically processed, then we would expect to see a Location effect but no interaction. Earlier experiments using simpler stimuli have suggested that peripheral stimuli are significantly influenced by spacing. Eriksen and Eriksen (1974) presented peripheral letters on either side of a target letter; when the former matched the latter, they found a significant facilitation effect. It is important to note that the size of this effect varied with between-letter spacing; the more white space between the priming letters, the more they decreased RT to the target word. The authors concluded that open spacing makes the peripheral letters more discriminable. In a related experiment, Mackworth (1965) found that perception of peripheral letters (displaced up to loo of visual angle) was virtually perfect when only one letter was shown in each visual field, but that adding extra letters or lines of letters sharply decreased recognition. Adding only one letter to the outside of the field decreased accuracy from 99% to 41%. These findings have important implications for arranging the format of a subliminal message. Because the majority of words in such a message will be peripherally registered to some degree, it seems important that they be surrounded by enough white space to be clearly distinguished. I t would also follow that simpler messages, having few words, are probably more effective than complex messages. To study this possibility, we presented the prompting message to both hemispheres in both a simple and complex form. For the former, we presented the words "PressIAvoid" 'fLeftlRightlf in both spaced and crowded formats. For the latter, we presented the message "Please/Do Not Press Your LeftlRight Hand," both spaced and crowded. If spacing makes a difference, we would expect that the simpler message would be more effective in general, and particularly when presented in the spaced format; that spaced formats would be more effective than crowded formats; and that Message should interact with Spacing.

.

Size and Shape of the Subliminal Window

129

EXPERIMENT IV METHOD

Subjects. Ten members of the Rutgers College community participated in the experiment - 4 men and 6 women. Ages ranged from 18 to 24. All Ss were right-handed with scores of 16 to 24 on the Edinburgh Inventory. Stimuli. Two lists of words were presented using, with minor exceptions, the same words presented in Experiment 111. The subliminal clue was presented at 30 msec. and always stimulated both visual fields. In Trial 1, it commanded the subject to "Press" or tfAvoidff (left visual field) 7tLeft77or "Right" (right visual field). Two levels of spacing were tested. In the more open condition, command and location were presented alone and the total stimulus subtended 6O of visual angle; in the more crowded condition, the nonwords "XXXX" were presented just before the command and just after the location, and the total stimulus subtended 9.8O of visual angle (see Figure 4 ) . Rllmsec) 1000

800 700

PRESS AVO10

*

LEFT RIGHT

xxxx

PRESS AVOlO

n

r

600 PRESS

AVOID

PRESS

OPEN Figure 4.

AVOlO

CROWDED

Experiment I V , Trial 1. Reaction time for correct recognition of the target word a8 a function of Command (PRESS

VS.

mode of presentation (open: 6';

crowded: 9 . 8 ' ) .

AVOID), key location (Left v8. Right), and

In Trial 2 , the stimulus was the sentence "DO Not/Please Press Your Right/Left Hand." I t spanned both visual fields (see Figure 5 ) . Two levels of spacing were tested. In the spaced condition, the sentence spanned the

D.P.Spence, L. Klein, and R.J. Fernandez

130

full width of the viewing field ( 1 4 O of visual angle). In the unspaced condition, the sentence began closer to the fixation point on the left and ended closer on the right ( l o o of visual angle). RTI msec) PLEASE

PRESS

*

YOUR

LEFT RIGHT

HANO

800 700 600

KEY

L R PLEASE

L R 00 NOT

L R PLEASE

NONWORO

CROWOEO

SPACED Figure 5.

L R 00 NOT

Experiment IV, Trial 2. Reaction time for correct recognition of the target word as a function of Command (PLEASE PRESS

VS.

DO NOT PRESS), key location (Left v8.

Right), and mode of presentation (spaced: 14';

crowded: 10').

On both trials, the eight conditions were distributed randomly over the 80 target words. Each set of 10 words was matched for word frequency and word length. Fifteen pronounceable nonwords were distributed randomly throughout the list and were preceded by a real word in both right and left visual field. Offset-onset interval remained the same as in Experiment 111 (230 msec.). Procedure. Same as Experiment 111 except that the target word was cued by a short tone created by the microcomputer. Recognition testing was slightly altered, and the new version is described below. RESULTS

All lexical choices were inspected first for accuracy. All errors were tallied, their times subtracted from the cell means, and new means were computed. A three-factor analysis of variance was used to reduce the data for Trial 1 and for Trial 2 ; the factors are Spacing, Command, and Location, Mean RTs are shown in Figures 4 and 5 averaged across subjects. (Two subjects were eliminated from Trial 2 because recognition testing

Size and Shape of the Subliminal Window

131

showed that they were partly aware of a significant number of subliminal clues. Trial 1. Main effect for Location was significant (F=16.06, p c .005, 1 / 9 d.f.1,

an indication that RTs to target words preceded by the word "Left" were significantly shorter (%=690 msec) than RTs preceded by the word "Right" (%=759msec). The difference of 69 msec. in this condition is somewhat less than the difference of 90 msec. reported in Experiment 111, and the accompanying F is appreciably smaller than the F in Experiment 111 (43.69). Location interacted significantly with clue spacing. In the more open condition when only two words were presented, the leftlright difference was much larger (93 msec.) than in the more crowded condition where i t dropped to 45 msec. The interaction between Location and Spacing yielded an F of 9.79, p c .025, 1 / 9 d . f . There was a significant interaction of Command with Location, but in a direction opposite from what was predicted. When the Location clues were they tended to further increase the differences that preceded by 1fAvoidv7, appeared when they were preceded by "Pressff (see Figure 5 ) . The interaction yielded an F of 13.25, p e .01, 119 d . f . Trial 2 . Main effect for Location was significant (F=28.20, p c .005, 117 d.f.1. Once again, RTs to target words were facilitated by the clue "Left" regardless of the other variables of Command or Spacing (% Left =694 msec. ;

E Right =755 msec.). Neither the size nor the significance of the difference matches the results of Experiment 111. Main effect for Command was marginally significant (F=4.54, p c .07,

117 d.f.1; the command "Please Press" resulted in shorter RTs than the command "DO Not Press" (see Figure 5). On the other hand, there was no evidence that Command interacted with Location (F=2.39, p>. 1 0 , 1 / 7 d . f. ) , and thus no evidence that the full sentence had been processed. What is more, Spacing did not interact with either Command or Location.

Recognition. After both lists had been presented, we sampled awareness of the subliminal clue by presenting the target word for a fixed period (500 msec.) and asking the subject to report the target word and, in addition, whatever else he had seen. None of the subjects were able to make out the complete clue on either trial. Correct recognition of specific clue parts is presented in Table 2 for each trial. It can be seen that on Trial 1 more

132

D.P.Spence, L. Klein, and R.J. Fernandez

information is picked up when the clues are presented alone than when they are accompanied by visual noise; that more clues are perceived in the right visual field than in the left; and that the word "Left" is slightly more visible than the word "Right." About the only finding of interest in Trial 2 is the recognition of the word "Press." Errors. Errors per subject ranged from 0 to 9 on Trial 1 and from 0 to 7 on Trial 2 . In both trials, more errors occurred when the target word was preceded by a misleading clue (tfRight'f). On Trial 1 , F for Location is 6.7, p c - 0 5 , 1/9 d . f . , and on Trial 2 . F for Location is 4.34, p c .08, 1 / 7 d.f. DISCUSSION The results from the first set of clues in Experiment IV tend to support the hypothesis that spaced formats are more effective than crowded formats. The results from both sets of clues support the hypothesis that what is registered in the right visual field takes precedence over what is registered in the left, and in neither trial do we find any evidence that both hemispheres can collaborate in processing a verbal message. In Trial 2 , Command did not interact with Location, and in Trial 1 , although we found an interaction. we also found that the effective meaning of 1'Press7' and "Avoid" was the opposite from what we would have predicted. Clearly, the effect of a stimulus which spans both visual fields cannot be predicted from the words alone; the effective stimulus under these conditions is apparently quite different from i t s literal meaning. We are on somewhat safer ground in trying to predict the effect of a stimulus in the right visual field but a long way from learning the meaning of stimuli in the left visual field, and equally in the dark in trying to understand the conditions under which the two visual fields can work together to process a sentence or phrase that falls on both sides of the fixation point. These findings have obvious implications for subliminal research. Because the left hemisphere appears to assume priority, it may be necessary to learn to "read" from right to left and become aware of the fact that the right side of the stimulus may assume semantic priority. Its meaning will either not be modiried by left-side stimuli (as in Trial 21, or it will be modified by a peculiar distortion of left-side stimuli (as in Trial 1 where ffAvoidTf was more facilitative than "Pressfr). It may also be true that leftside stimuli may actually interfere with right-side processing. The best ev-

Size and Shape of the Subliminal Window

133

idence for this statement comes from a comparison of Experiments 111 and IV. Only when both Command and Location were presented in the right visual field did we find a significant effect of the first on the second. To

share the same message between the two hemispheres (as in Experiment IV) would seem to eliminate the first part and limit the effect to the right side.

GENERAL DISCUSSION Choice of visual field would seem to place a much more significant restriction on the impact of the subliminal stimulus than distance from central fixation. With both simple and complex stimuli, it would not seem to matter (within the limits under study in the present set of experiments) whether the critical clues fall within the focal or peripheral regions of the viewing rield. Further experiments will be needed to determine the outer limits of this window, but it seems clear from the present data that words falling as tar a s

7O

from the fixation point can still be meaningfully processed (see

Experiments I and 11, and the Location effect in Experiment 111, right visual field). Which hemisphere is invoked is a much more important question, and this difference does not appear clearly until we move from simple to complex stimuli. In Table 3 , we have brought together the relevant data from Experiments 11, 111, and I V to show how effect size varies with complexity of stimulus and region of registration (only the 30 msec. conditions are included). Single words facilitated lexical decision equally well in both right and left hemispheres, with high associate primes producing a greater effect than low associate primes. When we moved from simple stimuli to the more complex phrase used in Experiment 111, w e found it to have considerably more effect when i t was presented to the left hemisphere than when i t was presented to the right. When a complex stimulus was presented to both hemispheres, we found no evidence for syntactic processing; the combined effect of command and location w a s either negative or not significant. It seems clear that the impact of a complex phrase can change significantly depending on whether it is presented entirely in the left visual field, half in left and half in right, or entirely in the right. changes, the role of eye fixation becomes crucial.

Because of these

D.P.Spence, L.Klein, and R.J. Fernondez

134

Table 3 Summary o f E f f e c t s of Cueing Stimuli Presented a t 30 msec. Left Hemisphere

Right Hemisphere

Facil.

Facil.

Eff.

Eff.

(meec.) -

F P -

(msec.) F P -

Unilateral

Single Words

*

(Exp. 11)

High Assoc.

122

12.48

.005

83

15.12

.005

Low Assoc.

43

3.02

.10

56

4.05

.05

6.66

.05

-7

Phrase (Exp. 111)

**

144

Bilateral

**

.04

.SO

Facil. Eff.

F P -(msec.)

Phrase (Exp. IV)

* **

** **

Trial 1

-78

13.25

.01

Trial 2

57

2.39

.10

Combined focal and p e r i p h e r a l e f f e c t s We computed t h e combined e f f e c t of Command and Location by s u b t r a c t i n g t h e Left-Right d i f f e r e n c e following t h e negative command from the Left-Right d i f f e r e n c e following the p o s i t i v e command.

Why is the left visual field not able to participate in syntactic processing when we have evidence (from Experiments I and 11) that it is capable of simple semantic priming? Zaidel (1983) reports that in two commissurotomy patients, the right hemisphere is somewhat impoverished relative to the left; simple words are "decoded consistently better than the longer phrases" and "syntactic structures are available but limited by load on short-term memoryTt ( p . 5 4 2 ) . If we apply these findings to the current

Site and Shape of the Subliminal Window

135

study, we could argue that some of the grammar necessary to parse the commands in Experiments I11 and I V is stored only in the left hemisphere. If the verb (when presented to the left of the fixation point) is first processed by the right hemisphere, it may be necessary to transfer its meaning to the language hemisphere before it can be coupled with the object (the words "Left" or "Right"). The time necessary for this transfer may exceed the offset-onset time of 230 msec., and as a result, we do not see any evidence of Command interacting with Location. But there is a further complication that is suggested by the results of Experiment I V , Trial 1. When the command "Avoid" preceded the words "Left" o r TIRight",we found a greater Location effect than when they were preceded by the command flPress.fl One way to understand these paradoxical findings is to argue that the right hemisphere is primarily responsive to such variables as word frequency, concreteness, and imagery. If an abstract o r infrequent word is presented, it may not be registered at all. From this rule we can conclude that "Avoid" may have been ignored, and thus the effective stimulus was either "Left" or 1fRight.f7But how do we account for the weak effect of "Press"? We have already argued that right hemisphere information cannot be used to modify left hemisphere information; the former may simply be represented as a rival stimulus which somehow competes with the meaning of the other parts of the message. Both "Press" and "Left"/"Right" may have been interpreted as separate and independent commands rather than as a verb modified by a noun. Assume that single-word processing can be accomplished equally well by either hemisphere. Then stimuli in the left visual field have a slight advantage because they arrive first at the right motor cortex which is the trigger point for a left-hand key press. Information about location would arrive slightly later, but if the "Press" command was obeyed, it could not affect choice of key. Thus the verb becomes an interfering stimulus which effectively obscures the information about location. Further interference seems to occur in the crowded condition where both 'lXXXX" and "Press" may have been processed before "Left"/ llRightqt(see Figure 5 ) . We are now in a position to return to the evidence presented in Table 1) and consider i t with enlarged understanding. Suppose that the subjects' fixation was always central. Then it is not surprising that the majority of the effects were non-signiricant because, in the first place, the full message could not be syntactically processed (Experiment I V , Trial 2 ) and. in the second place, because whatever was in the right side of the mes-

136

D.P. Spence, L. Klein, and R.J. Fernandez

sage and processed by the left hemisphere might be canceled by words in the left side (Trial 1). Only if fixation was maintained at the starting point of the message would we expect that complete (right visual field) processing would take place, and no subliminal experiment provided unambiguously for this possibility. What about those subliminal studies which report positive results with a complex message? It seems more than likely that such effects are carried by the right-side words in the stimulus which register in the right visual field (left hemisphere). I t may be no coincidence that the single significant finding tallied in Table 1 was provided by the Hebrew stimulus "MOMMY AND I ARB ONE", because only in this case (because of the right-to-left rules of the language) would M O M M Y be presented to the right visual field (left hemisphere). The significant results may have been a consequence of that accident. In all the other studies in Table 1, the critical parts of the message (MOMMY, DADDY, and BEATING) would be sent to the non-dominant hemisphere, and none of these results were significant. Whether we are correct in all aspects of this argument, it seems safe to conclude that a detailed knowledge of differential hemisphere processing is needed before we can predict the effects of a complex subliminal stimulus. As soon as the message impinges on both visual fields, its effective meaning will necessarily be quite different from its literal meaning - in other words, a message will mean one thing when foveally processed in the usual left-to-right manner, and quite another when i t is presented to focal and peripheral regions of the right and left visual fields. The significant aspect of subliminal processing may thus be less the factor of speed of exposure and much more the factor of region of registration. and up to this point, the first variable has not been separated from the second. Because region of registration has never been brought under experimental control, much of the unreliability in subliminal studies in general may stem more from problems of message processing than from problems of acuity and the consequences of reduced information. When region of registration (and the correlated variable of handedness) is brought under stricter experimental control, we may begin to see much greater regularity emerging from subliminal experiments. What, finally. is the relation between subliminal effects and the Freudian Unconscious? The verdict is still out. We have seen (in Experiments I11 and IV) that the effective stimulus may be significantly different from the stimulus as read, but the transformations may be less a function

Size and Shape of the Subliminal Window

137

of the primary process and more a consequence of peculiarities of hemisphere processing. Complex messages presented to the left visual field do not seem to be syntactically processed, and we might speculate (from Experiment 111) that what happens instead is that the more concrete words take precedence over the more abstract, and nouns take precedence over verbs. To what extent this effect is the result of region of registration will need to be explored in future studies. We also found (in Experiment

IV) that right-hemisphere information is not necessarily integrated with the left-hemisphere remainder of the message; as a result, the right side of the message sometimes takes precedence over the left, depending on the frequency and concreteness of the latter, and that where fixation happens to fall will significantly determine the impact of the stimulus. Consequences of eye position are clearly of a different order from consequences of the primary process, and it begins to appear as if the latter cannot be properly studied until we understand more about the former. A stimulus outside of awareness may be processed according to a quite different set of operotions than we find in conscious processing, but pains must be taken to make sure that the intended message reaches the processing centers with its meaning intact. We can then begin to study the ways in which its meaning is subsequently transformed by primary process or similar kinds of mechanisms. But unless an intact message reaches the higher centers,

none of these questions can ever be asked. Whatever the final standing of the primary process, it seems more parsimonious at the moment to assume that the unconscious system is content-free and that it should be distinguished from conscious processing largely along formal lines. This approach would suggest that brief stimuli are registered intact; that they are not automatically subject to the categorical transformations which are assumed to be part of the primary process; and that what appears as changes in form and meaning is due more to the effects of the visual processing system (and the subject's effort to make sense of these changes) than to something called The Unconscious. What are these formal differences? It might be useful at this point to summarize the main discrepancies between conscious reports (as gathered in the Recognition section of each experiment) and the subliminal and nearliminal priming effects, because at the very least, they support Marcel's hypothesis that "the structural languages of conscious representations are not directly mappable onto those of non-conscious representations, i.e. neither commensurate nor coextensive" (Marcel, 1983b, p. 2 5 6 ) .

p

they are

138

D.P. Spence, L. Klein, and R.J. Fernandez

1. In the faster part of Experiment I1 (30 msec. exposure), the priming effect was equally strong in both right and left visual fields, and in both focal and peripheral locations. On the other hand, correct identification of the priming stimulus signiticantly favored focal over peripheral primes ( p e .001) and right visual field over left visual ( p e .001). Marcel has suggested that conscious awareness results from the "imposition of a particular interpretation on what otherwise consists of multiple interpretations" ( p . 2431, and it may be that the pattern of correct identifications reflects a tendency (favored by reading) to sweep the visual field [after the query "WORD?") in a left-to-right direction. This tendency would favor the right visual field and (assuming a gradual decay of information) the right focal over the right peripheral field. But it is clear from the findings that recognition reports are not isomorphic with stimulus registration and should not be taken as necessarily indicative of the full spectrum of stimulus processing. 2 . A similar left-right bias was evident in Experiment I11 where recognition of the priming stimulus favored the right over the left visual field, and the left portion of each visual field (see Table 2 ) . There was a clear discrepancy between the very strong subliminal effects of Location ( p e ,001) and the failure of any subject to report seeing the words "Left" or "Right" in either visual field. Once again, correct recognition did not predict the precise form of the subliminal effect: once again, the information available to the subject in the priming part of the experiment was not adequately sampled by the recognition trials. 3. Another kind of discrepancy was manifested in Experiment I1 when we divided the subjects into two groups according to correct recognition and looked at the difference in priming effects. In neither the slow nor the fast condition did we find an interaction between awareness of the stimulus and degree of priming, which indicates that conscious awareness does not predict amount of subliminal priming, and which again suggests that what is consciously reported is not a simple transform of what is unconsciously available. And it is also well known that the kind of information gathered during recognition or threshold trials is extraordinarily sensitive to the questions being asked (and, by implication, to the expectation of the subject). 4 . In Experiment IV, Trial 2 , we found a clear preference for recognition of the command "Press" and no awareness of the location terms fTLeftttand llRight.ff Yet the priming effect was almost entirely accounted

Size and Shape of the Subliminal Window

139

for by the two location cues (see Figure 5) with a main effect for Location which was highly significant ( p < . 0 0 5 ) . Once again, conscious report does not represent all the information available. Not apparent from Table 3 but clearly evident during the recognition procedure was the difficulty experienced by the subject in trying to report on fleeting impressions and the way in which conventional categories were used to shape his or her sensory experience. Partial cues were more often reported as words than as strings of letters, and once a response was coded as a word, the same label tended to be used in subsequent trials, often in response to different cues. Fleeting left-hand cues were often located on the right (and it is this distortion which accounts in part for the strong right-side bias shown in Table 2 - the left-hand cues were underreported), and in Experiments I and 11, the somewhat more unusual primes were often distorted to make rather common words. These are not systematic data, but our overall impression docs support the assumption that conventional categories (equivalent to Marcel's "culturally given presuppositions") played a strong role in giving final form to the subject's conscious sense impression. It is worth noting, in conclusion, how these conventions were implid t l y missing from unconscious processing of the same stimuli. The content of the more unusual primes was maintained intact, for otherwise a facilitated response to the associated target word would not have appeared. The predominant right-side bias was not in effect, and primes in both Visual fields were equally effective. Most impressive of all, the overriding preference for focal over peripheral registration was set aside with the result that offsets of T o to left and right of fixation did not prevent the meaning of the prime from being registered and influencing the subsequent lexical decision. Data such as these would suggest that information processing outside of awareness is exquisitely responsive to a full range of stimulus vanations and that information filtered through conscious reports tells us more about stereotype and convention than about the true capacity of the sensory system.

140

D.P.Spence, L.Klein, and R.J. Fernandez NOTE

1)

Eye movements were not monitored during the experiment and the skeptical reader might ask how we can be sure that central fixation was maintained during the lexical decision trials. We draw attention, first, to the fact that position of the prime was always changing, and no two successive locations were the same. Second, it is well established that the latency of saccadic eye movements is of the order of 180 to 250 msec. (see Haber and Hershenson, 1973, p. 207). Third, it is known that saccadic eye movements are ballistic in that path and distances are determined prior to movement. If a fixation were caused by a brief peripheral stimulus, the eye would first fixate the stimulus and then return to the center of the screen in order to process the word. The two saccadic movements would each consume about 200 msec. Thus, a failure to maintain central fixation would increase lexical decision time by at least 400 msec. and add substantial variance to the data, thus reducing the chances of finding significant differences. It would seem to follow that the facilitation effects reported here must come about as a result of priming caused by stimuli which were presented to specific parts of the peripheral visual field and which could not be centrally fixated. It might also be argued that the exposure speeds used in these studies are not truly subliminal because the stimulus could sometimes be identified. We were constrained in this respect b y the limitations of the Apple micro-computer which does not permit exposures much below 25 msec.; future studies, using a somewhat different technology, will explore the lower limits of the exposure continuum. It should be kept in mind, however, that shorter exposure speeds would not affect region of registration; differences due to visual field or degree of offset should continue to appear, If syntactic processing, for example, fails to take place in the right hemisphere at 30 msec., it seems unlikely that it will begin to reappear at 4 msec.

Size and Shape of the Subliminal Window

141

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