Comparisons of reaction time patterns in a sequential visual recognition task with simple geometric forms

Right isosceles triangles, which differed in size and orientation, were presented in a sequential visual recognition task. Subjects produced an identity match response if the first self-presented stimulus, now in memory, was identical to a sequentially presented stimulus and a nonidentity match response if the subsequently presented stimulus differed in either or both size and orientation. The pattern of nonidentity recognition reaction times produced was compared to predicted patterns deduced from several theories of form information processing. The pattern of responses for both group and individual data were better described by serial and parallel self-terminating models with probabilistic assumptions than they were by template or deterministic serial or parallel models. A second study, in which identity and nonidentity response bias was equated, found that the identity responses were significantly faster than nonidentity responses, supporting wholistic processing for the identity matches and, when combined with the nonidentity match results, supporting a dual process theory.     

Duration estimates of two information processing components

Adult humans attempted to make quick responses to the first of two sequentially presented visual stimuli. At short interstimulus intervals (less than about 100 msec) accuracy was impaired by a different second stimulus and this was hypothesized to reflect the activity of an information processing component concerned with stimulus registration. At longer interstimulus intervals (up to approximately 350 msec) reaction time was inhibited by a different second stimulus and this was assumed to reflect the activity of a second component concerned with decision. The stimulus registration component was insensitive to variations in the complexity of the task, while the decision component was found to be greater for a task requiring recognition (is the current stimulus the same as an earlier one?) than for one merely requiring choice (what is the current stimulus?). This functional independence and the sizeable difference in the temporal range of susceptibility led to the conclusion that two distinct information processing components were involved.     

Processing emotional stimuli: Comparison of saccadic and manual choice-reaction times

We compared the speed of discrimination for emotional and neutral faces in four experiments, using a forced-choice saccadic and manual reaction time task. Unmasked, brief (20 ms) bilateral presentation of schematic (Exp. 1) or naturalistic (Exp. 2) emotional/neutral face pairs, led to shorter discrimination of emotional stimuli in saccadic localisation task. When the effect of interference from emotional stimuli is ruled out by showing a pairing of the emotional or neutral face with an outline face, faster saccadic discrimination was obtained for fearful facial expression only (Exp. 3). The manual discrimination reaction time was not significantly different for emotional versus neutral stimuli. To explore the absence of a manual RT effect we manipulated the stimulus duration (20 ms vs. 500 ms: Exp. 4). Faster saccadic discrimination of emotional stimuli was observed at both durations. For manual responses, emotional bias was observed only at the longest duration (500 ms). Overall, comparison of saccadic and manual responses shows that faster discrimination of emotional/neutral stimuli can be carried out within the oculomotor system. In addition, emotional stimuli are processed preferentially to neutral face stimuli.     

Decisional processing in paranoid and non-paranoid schizophrenics

40 schizophrenic subjects, divided into paranoid/non-paranoid categories and 14 normal controls were presented a task which involved making "same-different" judgments during random presentations of a series of visual comparison stimuli with a standard which represented the midpoint of the stimulus continuum. Using Sternberg's Choice RT paradigm for studying the locus of cognitive deficit, difficulty at the response-selection stage was manipulated while holding other stages constant. It was predicted that paranoids would have shorter RTs at easy decision points and longer RTs at difficult decision points relative to non-paranoids. The directions of the differences were as predicted but did not attain statistical significance. Both schizophrenic groups, compared to normals, made significantly fewer "same" responses on those trials where the comparison and standard were most similar.     

Stroboscope motion: Effects of duration and interval1

The quality of stroboscope motion induced by the successive presentation of two illuminated squares obeys two rules. For all stimulus durations shorter than 100 msec, optimal motion occurs when the stimulus onsets differ by about 120 msec. For stimulus durations longer than 100 msec, optimal motion occurs when the second stimulus begins at the termination of the first stimulus. The two rules relating quality of motion to duration suggest a single principle, namely, that the quality depends only on the interval between the visual responses to the two stimuli. The interresponse interval at which motion is optimal is independent of stimulus duration.     

Associative strength effects in the lexical decision task

Four experiments explore the role of automatic and attentional processing in producing strength effects in a lexical decision task. Experiment I manipulated the relative proportion of related and unrelated pairs, the stimulus-onset-asynchrony (SOA), and the strength of the prime-target relationship. Results indicated that strength was independent of the proportion of related and unrelated pairs and SOA. Experiment 2 manipulated the relative proportion of strong and weak related pairs and the strength of the prime-target relationship at a relatively long SOA interval (500 msec). Results showed that the strength effect was present when more strong than weak pairs were presented, and it was absent when the stimulus list contained more weak than strong pairs. Experiment 3 replicated the more weak pairs condition of Experiment 2 but with a short SOA interval (100 msec) and showed that the strength effect was found regardless of the large number of weak related pairs presented. Experiment 4 manipulated strength of the prime-target relationship and proportion of strong and weak pairs but introducing a neutral prime condition and a longer SOA interval (1000 msec). Results are discussed within a two-process model (Posner & Snyder, 1975) postulating that the strength effect at short SOAs is due to automatic processes, whereas at long SOAs it is due to the influence of attentional processes.     

Emergence of symmetry in a visual conditional discrimination by chimpanzees (Pan troglodytes)

In Exp. 1, three young chimpanzees were trained to match red to a cross and green to a circle in an arbitrary matching-to-sample task. After acquisition of this task, they were tested for the emergence of associative symmetry of these conditional relations using the trials on which shapes were presented as samples and colors as comparisons. One of the three chimpanzees showed statistically significant accuracy on these test trials. This successful subject served in Exp. 2, in which an auditory-visual stimulus appeared contingent upon red and a cross while another auditory-visual stimulus was contingent upon green and a circle. This subject showed higher accuracies in symmetry tests than in Exp. 1, which suggested the facilitative effects of these events common to sample and correct comparison on the development of symmetry. In Exp. 3, subsequent tests in which only these stimuli were presented as samples indicated that these stimuli might have become the members of equivalence classes.     

Binary-choice decision time depends upon cerebral hemisphere and nature of task

Binary-choice paradigms are classificatory problems of basic importance to the understanding of elementary decision processes. Generally when subjects decide if two visual stimuli are identical or differ by as little as one element, the decision of "Different" takes longer. This finding is unexpected as decisions of "Different" should not require an exhaustive matching of elements. Using stimulus presentation to the right and left cerebral hemispheres, the right hemisphere initiated fast selections of "Same" for figural material and alone was responsible for the "Same"/"Different" response differential. Exp. 1 (n = 22) gave no differences for same-different, unilateral-bilateral stimulation, and left-right hemispheres. Exp. 2, using word meaning as the binary-choice task, also showed faster decisions for "Same" but a different left-hemisphere-dependent strategy. The nature of information processing in relation to binary-choice tasks is discussed and the utility of bihemispheric paradigms is demonstrated.     

Function transformation without reinforcement

In studies of function transformation, participants initially are taught to match stimuli in the presence of a contextual cue, X; the stimuli to be matched bear some formal relation to each other, for example, a relation of opposition or difference. In a second phase, the participants are taught to match arbitrary stimuli (say, A and B) in the presence of X. In a final test, A often displays behavioral functions that differ from those of B, and can be predicted from the nature of the relation associated with X in the initial training phase. Here we report function-transformation effects in the absence of selection responses and of their reinforcers. In three experiments with college students, exposure to relations of difference or identity modified the responses given to later stimuli. In Experiment 1, responses to a test stimulus A varied depending on preexposure to pairs of colors that were distinct from A but exemplified relations of difference or identity. In Experiment 2, a stimulus A acquired distinct functions, depending on its previous pairing with a contextual cue X that had itself been paired with identity or difference among colors. Experiment 3 confirmed the results of Experiment 2 with a modified design. Our data are consistent with the notion that relations of identity or difference can serve as stimuli for Pavlovian processes, and, in compound with other cues, produce apparent function-transformation effects.     

Whole and part comparisons of words and nonwords

Under conditions of sequential presentation, two words are matched more quickly than are a single letter and the first letter of a word. An exception to this whole-word advantage was reported in 1980 by Umansky and Chambers, who used word pairs as stimuli, and asked subjects to compare the entire words or the words’ first letters. Experiment 1 showed that the stimulus lists used by Umansky and Chambers may not have constrained subjects to process the displays differently for wholistic and component comparisons. In those studies, the two words were identical onsame trials for both wholistic and first-letter comparisons, so that first-letter decisions could have been based on wholistic information. In the present study, lists were constructed so that first-letter decisions could not be determined correctly by wholistic information (e.g., BLAME/BEACH), and the whole-word advantage was replicated. Experiment 2 tested whether wholistic comparisons are generally superior to component comparisons. For consonant strings, first-letter comparisons were made more quickly than were whole-string comparisons. These results are interpreted as support for hierarchical models of visual word processing.     

Effects of relation similarity on part-whole decisions

Subjects were presented with word pairs (e.g., bed-mattress) and timed as they decided whether one word named part of the item named by the other word. Yes responses were facilitated, and no responses were impeded, by relation similarity (i.e., the similarity of the relation between the two stimulus items to the part-whole relation). Item similarity, the similarity of the two stimulus items to each other, had no effect. The results support the view that similarity effects in semantic decision tasks are due to the comparison of elements of the relation between the two stimulus words against relation elements that serve as criteria for the target relation that the subject has been asked to identify.     

Time course of amodal completion revealed by a shape discrimination task

We measured the extent of amodal completion as a function of stimulus duration over the range of 15–210 msec, for both moving and stationary stimuli. Completion was assessed using a performancebased measure: a shape discrimination task that is easy if the stimulus is amodally completed and difficult if it is not. Specifically, participants judged whether an upright rectangle was longer horizontally or vertically, when the rectangle was unoccluded, occluded at its corners by four negative-contrast squares, or occluded at its corners by four zero-contrast squares. In the zero-contrast condition, amodal completion did not occur because there were no occlusion cues; in the unoccluded condition, the entire figure was present. Thus, comparing performance in the negative-contrast condition to these two extremes provided a quantitative measure of amodal completion. This measure revealed a rapid but measurable time course for amodal completion. Moving and stationary stimuli took the same amount of time to be completed (≈ 75 msec), but moving stimuli had slightly stronger completion at long durations.     

An orientation illusion analog to the rod and frame: Relational effects in the magnitude of the distortion

In previous studies, we have measured individual differences in simultaneous brightness discrimination between a long-duration (500 msec or more) comparison pulse and a set of briefer test pulses of the same luminance. Some observers judge the comparison pulse to be brighter than all test pulses in a range from 20 to 320 msec. Other observers exhibittemporal brightness enhancement: a test pulse of 80 msec for our stimulus conditions is judged brighter than the comparison pulse. Individual differences depend upon the temporal asynchrony between test and comparison pulses. Observers designated Type A show temporal brightness enhancement for both simultaneous onset of test and comparison pulse and for simultaneous offset of the pulses. Type B observers exhibit brightness enhancement for simultaneous offset of pulses but not for simultaneous onset. Type C observers do not exhibit brightness enhancement effects. Here we use both short (80 msec) and long (640 msec) pulses as the comparison stimuli. We replicate our previous pattern of individual differences for the long comparison stimulus. For the short comparison stimulus, brightness discrimination functions for the three classes of observers are exactly predicted from the patterns obtained with the conventional long comparison pulse. This confirms the generality of individual differences in pulse brightness perception and shows that they do not depend upon the particular stimulus conditions selected for the discrimination task.     

Subjective shortening in humans' memory for stimulus duration

Three experiments investigated memory for stimulus duration in humans using a modification of a delayed-matching technique previously used to study event memory in pigeons. In a session of 48 discrete trials subjects were presented with a sample stimulus (a 500-Hz tone with mean duration of 400 msec) then a comparison stimulus (the same duration as the sample, or longer or shorter), after a delay that was 1 to 10 sec in Experiments 1 and 2, and 2 to 16 sec in Experiment 3. After the comparison had been presented, subjects judged whether the sample and comparison had the same duration (a YES/NO decision, Experiment 1), or whether the comparison was longer, shorter, or of the same duration as the sample (Experiments 2 and 3). Overall, mean number of correct responses changed little with increases in the delay, but the change of number of correct responses with delay was markedly different on trials in which the sample and comparison were the same, the comparison was shorter, or the comparison was longer. In general, accuracy declined with increasing delay in the first case, remained constant in the second case, and increased when the comparison was longer than the sample. Examination of the types of errors made on the different sorts of trials (Experiment 3) suggested that the data were produced by two mechanisms: (1) subjective shortening of the sample as the delay between sample and comparison increased, and (2) a time-order error to respond that the sample was longer than the comparison. Overall, it appears that humans' working memory for duration exhibits a subjective shortening effect similar to that previously found in pigeons.     

Directed attention prolongs the perceived duration of a brief stimulus

Stelmach, Herdman, and McNeil (1994) suggested recently that the perceived duration for attended stimuli is shorter than that for unattended ones. In contrast, the attenuation hypothesis (Thomas & Weaver, 1975) suggests the reverse relation between directed attention and perceived duration. We conducted six experiments to test the validity of the two contradictory hypotheses. In all the experiments, attention was directed to one of two possible stimulus sources. Experiments 1 and 2 employed stimulus durations from 70 to 270 msec. A stimulus appeared in either the visual or the auditory modality. Stimuli in the attended modality were rated as longer than stimuli in the unattended modality. Experiment 3 replicated this finding using a different psychophysical procedure. Experiments 4-6 showed that the finding applies not only to stimuli from different sensory modalities but also to stimuli appearing at different locations within the visual field. The results of all six experiments support the assumption that directed attention prolongs the perceived duration of a stimulus.     

The effects of negative relatedness upon word-picutre and word-word comparisons and subsequent recall.

In two experiments subjects were required to compare the meanings of either a word and a picture, or of two words. Different name levels, i.e. category versus superordinate names, had only a small effect on the time to compare a name with a picture. When incongruent stimulus pairs were semantically related, both positive and negative decision times were longer than when the incongruent pairs were unrelated; relatedness also affected subjects' recall of stimuli. Implications for models of semantic decision are discussed.     

Visual perseveration in normal and mentally retarded children

Visual perseveration was investigated within mentally retarded and second, fifth, and eighth grade normal children (Ns = 12 each group). Subjects matched an auditorially presented click to the onset and offset of visually presented stimuli. Time differences between visual stimulus offset and the point at which subjects reported simultaneity of the click and visual stimulus offset was assumed to reflect visual perseveration. Results showed: (a) no differences between the normal children as a function of age; (b) no difference between groups for stimuli of 100 msec. or longer duration; and (c) retarded subjects judged stimuli of 20 and 50 msec. to be of shorter duration than did normal subjects. This highly specific distinction between retarded and normal subjects suggests a difference in an early stage of perceptual processing.     

The activation of semantic memory: Effects of prime exposure,prime-target relationship,and task demands

Priming facilitation was examined under conditions of brief incremental prime exposures (28, 43, 71, and 199 msec) under masked conditions for two types of lexical relationships (associative-semantic pairs, such as "wolf-fox," and semantic-feature pairs, such as "whale-dolphin") and in two tasks (primed lexical decision and semantic categorization). The results of eight experiments revealed, first, that priming elicits faster response times for semantic-feature pairs. The associative-semantic pairs produced priming only at the longer prime exposures. Second, priming was observed earlier for semantic categorization than for the lexical decision task, in which priming was observed only at the longer stimulus onset asynchronies. Finally, our results allowed us to discredit the congruency hypothesis, according to which priming is due to a common categorical response for the prime and target words. The implications of these results for current theories of semantic priming are discussed.     

Effects of visual-field and matching instruction on event-related potentials and reaction time

Vertical letter pairs were presented randomly in the left and right visual hemifields in a physical identity match and name identity match condition. The reaction times showed a right visual field superiority for name matches, and a left visual field superiority for physical matches. Event-related potentials to letter pairs showed a sequence of three waves: a negative wave (N2, around 270 msec), a positive wave (P3, around 500 msec), and a broad positive slow wave (SW, around 600-700 msec), respectively. P3 and SW amplitudes were consistently larger at the left hemisphere than at the right hemisphere, regardless of the field of stimulation. At both hemispheres, N2 waves were always larger to stimuli presented in the visual field contralateral to a hemisphere than stimuli presented in the visual field ipsilateral to a hemisphere. The positive waves (P3, SW) showed the opposite pattern: smaller amplitudes to stimuli that were presented contralaterally than stimuli that were presented ipsilaterally to a given hemisphere. These results were attributed to a shift in sustained negativity on the directly stimulated hemisphere, relative to the indirectly stimulated hemisphere, reflecting either sensory at attentional processes in the posterior cerebral hemispheres.     

Learning mechanisms in matching to sample.

A model system and an experiment on early learning and decision processes in matching-to-sample and oddity-from-sample tasks are presented. The model system is based, in part, on videotaped records of pigeons' looking responses before they chose 1 of 2 comparison stimuli. In order to see the wavelength stimuli recessed behind the pecking keys, the pigeons had to move in front of them. Although there were slight increases in the acceptance probability with switches between the stimuli before a choice response, the overall decision strategy was close to a Markov choice process in which choice proportions could be predicted by the product of each rejection probability and the final acceptance probability. Learning involved learning to discriminate rather than learning to adopt a stricter criterion for an acceptable sample match.