Pattern uncertainty and the discrimination of visual patterns

Sixty Ss individually sorted eight decks of 50 cards each. A deck contained 25 cards each of two stimulus patterns. The patterns were drawn from different sets of five-dot patterns judged to be equivalent. The eight decks represented pairs of patterns drawn (a) from the same equivalence set, (b) from different equivalence sets of the same size, and (c) from different equivalence sets of different sizes. Sorting times were shown to increase with increasing size of equivalence set, and were shown to be greater for patterns drawn from within the same equivalence set than for patterns drawn from different equivalence sets. Ratings of pattern goodness were found to be useful predictors of sorting time only in their capacity to discriminate between equivalence sets of different sizes. The results were interpreted as supporting the importance of equivalence set membership in a discrimination task where the S logically does not have to consider stimuli other than the given criterion stimuli.     

Memory search instead of template matching? Representation-guided inference in same-different performance

Data from two experiments using transformationally related patterns forming rotation/reflection equivalence sets of different size's are presented. In a same-different experiment, two successively presented patterns were judged as same when they belonged to the same equivalence set, and different otherwise. Reaction times depended on the size of the equivalence set to which the patterns belong. This was the case, even when they were physically identical. Results are interpreted within a framework of memory-guided inference which assumes that participants perform a memory search within the equivalence sets activated by the compared patterns instead of comparing these directly. In Experiment 2, goodness ratings were required which are shown to reflect a second component of information processing.     

Visual recognition under conditions of high and low discrimination redundancy

The purpose of this investigation was to measure the minimum interval for recognition under conditions of high and low discrimination redundancy. The minimum interval for recognition is the briefest interval between two stimuli at which the first stimulus can be processed. Two sets of four digits were used. Digits were selected so that one set exhibited high discrimination redundancy and the other low discrimination redundancy. Ten Ss viewed digits with high discrimination redundancy, and 10 Ss viewed digits with low discrimination redundancy. The minimum interval for recognition for Ss tested with high discrimination redundancy was nearly twice as large as the minimum interval for recognition of the digits with low discrimination redundancy.     

A new approach to the formation of equivalence classes in pigeons

Four pigeons were given simultaneous discrimination training with visual patterns arbitrarily divided into two sets, with the stimuli in one set designated A1, B1, C1, and D1 and those in the other set designated A2, B2, C2, and D2. In sequentially introduced training phases, the pigeons were exposed to a series of reversals to establish AB and then CD equivalences. In subsequent testing sessions, a subset of stimuli from one set served as positive stimuli and those from the other set as negative stimuli on training trials, and transfer of the reinforced relation to other members of the sets was tested with nonreinforced probe trials. The pigeons were trained further on AC and BD equivalences and then were tested for the emergence of untrained AD and BC equivalences. Two of the 4 pigeons exhibited the emergence of one of these untrained equivalences, evidence for the emergence of transitive relations. This finding suggests that the pigeons established three-member functional equivalence classes by incorporating separately trained multiple equivalence relations. Repeated reversal training and probe testing enabled us to explore the formation and expansion of functional equivalence classes in pigeons.     

Effects of differences between stimuli, responses, and reinforcer rates on conditional discrimination performance

In a discrete-trial conditional discrimination procedure, 4 pigeons obtained food reinforcers by pecking a key with a short latency on trials signaled by one stimulus and by pecking the same key with a long latency on trials signaled by a second stimulus. The physical difference between the two stimuli and the temporal separation between the latency values required for reinforcement were varied factorially over four sets of conditions, and the ratio of reinforcer rates for short and long latencies was varied within each set of conditions. Stimulus discrimination varied directly with both stimulus and response differences and was unaffected by the reinforcer ratio. Sensitivity to reinforcement, estimated by generalized-matching-law fits to the data within each set of conditions, varied directly with the response difference but inversely with the stimulus difference arranged between sets of conditions. Because variations in stimulus differences, response differences, and reinforcer differences did not have equivalent effects, these findings question the functional equivalence of the three terms of the discriminated operant: antecedent stimuli, behavior, and consequences.     

Transformation-invariant cues in the recognition of simple visual patterns

Two alternative hypotheses about the discriminative cues in visual patterns were tested by comparing the speed with which Ss could apply two different classification rules for identifying a set of 16 simple dot patterns, consisting of four groups of four transformations. One rule required discrimination between groups of transformations, and another rule required discrimination between transformations within groups. The patterns within a transformation group were less similar in their positioning of dots than were patterns of the same transformation in different groups. Speed of identification, however, was more rapid for the discrimination between groups than for the discrimination of transformations within groups and was also invariant with respect to the specific transformations included in the same category under the between-groups classification rule. The discriminative cues in these patterns were thus indicated to be relationships among dots that remained invariant under the group of transformations.     

Parallel processing of the attributes of single stimuli

Three experiments are described, in which Ss had to decide whether or not single stimuli, varying along the dimensions of shape and color, satisfied a given criterion. In different conditions, the number of dimensions relevant to the criterion was varied. The first experiment indicates that simple interpretations of a standard Nickerson procedure are potentially artifactual. In the last two experiments, a design involving different difficulties of discrimination was used so that a serial interpretation of the results could be convincingly rejected, even for unpracticed Ss. These results strongly support the view that perceptually parallel processing normally occurs in the identification of single multidimensional stimuli. By this interpretation, apparently similar tasks may produce different patterns of results because of the use of different decision processes by the Ss.     

Functional equivalence classes in rats: Repeated olfactory discrimination reversals and delayed stimulus probes

The simultaneous matching-to-sample procedures that are widely used to study stimulus equivalence in human participants have generally been unsuccessful in animals. However, functional equivalence classes have been demonstrated in pigeons and sea lions using a concurrent repeated reversal discrimination procedure. In this procedure, responding to one set of stimuli is reinforced but responding to a different set is not and the set associated with reinforcement is changed with multiple reversals during the experiment. The experiments reported here were designed to assess whether functional equivalence classes could be demonstrated in rats using similar techniques. Rats were initially trained with two sets of olfactory stimuli (six odors/set). Following many reversals, probe reversal sessions were conducted in which rats were exposed to a subset of the members of each set and, later in the session, the withheld stimuli were introduced. Responding to these delayed probe trials in accord with the reversed contingencies constituted transfer of function. There was some evidence of transfer in Experiment 1, but the effects were relatively weak and variable. Experiment 2 introduced procedural changes and found strong evidence of transfer of function consistent with the formation of functional equivalence classes. These procedures offer a promising strategy to study symbolic behavior in rodents.     

Matching patterns vs matching digits: The effect of memory dependence and complexity on “same”-“different” reaction times

Two experiments are reported in which “same”-“different” reaction times (RTs) were collected to pairs of stimuli. In Experiment 1 stimuli were matrix patterns, and in Experiment 2 stimuli were digits. In both experiments, the pairs were presented simultaneously (discrimination task) and successively (memory task) for a set of nine simple and a set of nine complex stimuli. The following results were obtained: discrimination RTs were longer than memory RTs; RTs to complex stimuli were longer than RTs to simple stimuli; “same” RTs were faster than “different” RTs across all conditions except simple pattern discrimination, for which “different” RTs were faster than “same” RTs; and discrimination RTs for complex patterns were longer than would be predicted from the other conditions. Some evidence was obtained that the form of encoding for both patterns and digits in the memory task was visual. These results are discussed in terms of encoding and comparison strategies.     

Frequency and coding responses in verbal discrimination learning

Ss were given a verbal discrimination task where correct and incorrect stimuli appeared in one, two. or four different pairs in a within-Ss design. For a group tested with the usual anticipation procedure, correct repetitions helped and incorrect repetitions hurt performance. The pattern of results suggested that frequency is a salient cue in verbal discrimination learning but that coding or paired-associate processing may occur at the same time. Data from a second group of Ss for which frequency was a less salient cue gave more direct evidence for coding.     

Effects of training condition on the contribution of specific items to relational processing in baboons (Papio papio)

Relational processing involves learning about the relationship between or among stimuli, transcending the individual stimuli, so that abstract knowledge generalizable to novel situations is acquired. Relational processing has been studied in animals as well as in humans, but little attention has been paid to the contribution of specific items to relational thinking or to the factors that may affect that contribution. This study assessed the intertwined effects of item and relational processing in nonhuman primates. Using a procedure that entailed both expanding and contracting sets of pictorial items, we trained 13 baboons on a two-alternative forced-choice task, in which they had to distinguish horizontal from vertical relational patterns. In Experiment 1, monkeys engaged in item-based processing with a small training set size, and they progressively engaged in relation-based processing as training set size was increased. However, in Experiment 2, overtraining with a small stimulus set promoted the processing of item-based information. These findings underscore similarities in how humans and nonhuman primates process higher-order stimulus relations.     

The effects of complexity on the perception of vibrotactile patterns.

Vibrotactile patterns were presented to subjects' left index fingerpads using the array from the Optacon. A set of simple (one-line) patterns and a set of complex (two-line) patterns were constructed so that they were equally identifiable when presented individually. In Experiment 1, discrimination performance was lower for two-line patterns than for one-line patterns. Communality, the number of lines that two patterns share in common, appeared to be the major factor in reducing discrimination performance for two-line patterns. Experiment 2 measured the time required to identify individual patterns. There was no significant difference in identification times for one- and two-line patterns, suggesting that features within a pattern were processed simultaneously. In the presence of a temporal masking stimulus (Experiment 3), two-line patterns were more difficult to identify than one-line patterns, but reaction times were similar for the two sets of patterns. The results suggest that varying complexity affects perception of patterns at later stages of processing.     

Pythagorean distance and the judged similarity of schematic stimuli

Independent groups of Ss rated the similarity of pairs of patterns belonging to the same class, either bef ore or af ter a discrimination task of schematic concept formation (SCF). Mean similarity increased as a function of SCF pretraining. A linear relationship was found between a Pythagorean distance measure on the patterns and subjective similarity of pairs of stimuli (r=.88). No such relationship was obtained from an analysis of judgments from a group that viewed random, nonschematic stimuli. A secondary analysis of the discrimination judgments in the SCF task showed that the Pythagorean distance measure was predictive of judgments on pairs of stimuli from the same schema family, but the relationship did not hold for pairs representing two different schemata. Multidimensional scaling analyses indicated that mildly deviant schematic stimuli were perceived to be instances of a single family. The dimensions describing a schema cluster appeared to be specific to the sample of stimuli. A tendency for the Kruskal procedures to collapse certain types of stimulus clusters was observed and discussed.     

Generalization of cross-modal stimulus equivalence classes: operant processes as components in human category formation.

This study employed a stimulus-class rating procedure to explore whether stimulus equivalence and stimulus generalization can combine to promote the formation of open-ended categories incorporating cross-modal stimuli. A pretest of simple auditory discrimination indicated that subjects (college students) could discriminate among a range of tones used in the main study. Before beginning the main study, 10 subjects learned to use a rating procedure for categorizing sets of stimuli as class consistent or class inconsistent. After completing conditional discrimination training with new stimuli (shapes and tones), the subjects demonstrated the formation of cross-modal equivalence classes. Subsequently, the class-inclusion rating procedure was reinstituted, this time with cross-modal sets of stimuli drawn from the equivalence classes. On some occasions, the tones of the equivalence classes were replaced by novel tones. The probability that these novel sets would be rated as class consistent was generally a function of the auditory distance between the novel tone and the tone that was explicitly included in the equivalence class. These data extend prior work on generalization of equivalence classes, and support the role of operant processes in human category formation.     

Two types of phenomenal instructions for size and distance judgments of objects presented on a two-dimensional plane

Demand characteristics were studied in a simple situation in which observers made size and distance estimates of stimuli presented on a two-dimensional linear perspective drawing. Half the Ss were asked questions stressing phenomenal report: The other half were asked the same questions preceded by instructions stressing the objective nature of the stimulus configuration but requesting, nonetheless, phenomenal report. Instructions resulted in a significantly greater perspective size illusion but did not affect the distance estimates. No meaningful correlations between size and distance estimates were found.     

Individual pattern representations are context independent, but their collective representation is context dependent.

We studied context dependency of the representations underlying perceptual "goodness". Three experiments used a same-different task with classical Garner 5-dot patterns presented with an interstimulus interval (ISI) of 500 ms. Same patterns were allowed to be rotated or reflected versions of each other. Pattern goodness was varied according to rotation and reflection equivalence, using Garner's equivalence set size (ESS) measure. The ESS of both first and second patterns affected reaction time and accuracy. A model based on assumptions that Garner's equivalence sets constitute the generic representation of these patterns and that items within these sets are accessed serially was fitted to the data. Excellent fits were obtained, which were robust against frequency-induced bias at the level of the individual pattern, but sensitive to such bias at the level of the equivalence set. It was concluded that individual pattern representations are context independent, whereas their collective representations are context dependent. Simplicity and likelihood principles, therefore, seem to apply to different levels of a representation hierarchy.     

Sources of stimulus control during multiple discriminations

Pigeons learned to respond to the middle-sized member of six or seven sets of three stimuli differing in size. The sets were used successively, each serving as the discrimination problem from 10 to 16 times. After attaining criterion with one set, the birds received the others as probes. The number of responses in probes was related to the similarity of the probes to the prevailing discrimination problem. The birds responded either to the probe stimulus to which responding had most recently been reinforced, or to the probe stimulus closest in size to the positive member (S+) of the prevailing discrimination problem. Responses to a middle-sized probe-set stimulus occurred when it was the probe-set member most recently correlated with reinforcement, when it was one of two stimuli closest in size to S+, and when the stimulus closest in size to S+ was a negative member of the discrimination problem. All of the behavior could be explained in terms of control by the absolute sizes of the various stimuli.     

Corners,receptive fields,and visually evoked cortical potentials

Alternating stimuli with herringbone patterns were used to obtain visually evoked cortical potentials (VECPs) from three human Ss. Two sets of stimulus patterns were used, one with sharp corners and one with the corners rounded off. Each set ranged in angularity from 180 to 45 deg in 45-deg steps. Results showed that: (a)VECP response amplitude was greatest for the 90-deg-corner pattern, (b) response amplitude was greater for the 45-deg-corner pattern than for the 135-deg-corner pattern, and (c) cornered and rounded patterns evoked responses of greater amplitude than those evoked by the straight (180-deg) patterns. Also, the peak latency of responses to cornered patterns was shorter than that of responses to rounded and straight patterns.     

Effect of observing response requirements to sample and comparison stimuli on the establishment of reject control (sample/S- relations)

The establishment of sample/S- relations (or reject control) during conditional discrimination training (AB, BC) affects transitivity (AC), equivalence (CA) and reflexivity (AA, BB, CC) test outcomes. The present study parametrically evaluated the effects of different observing patterns to comparison stimuli on the establishment of reject control during baseline conditional relation training. A matching-to-sample with observing requirements (MTS-OR) procedure was implemented during AB and BC conditional discrimination training. During training, the participants were required to observe the sample and incorrect comparison on every trial before responding. In addition, the participants were divided into three groups that differed regarding the percentage of training trials on which they were prevented from observing the correct comparison stimuli: 25%, 50%, and 75%. Once the mastery criteria were achieved during training, transitivity (AC), symmetry (BA, CB), equivalence (CA), and reflexivity (AA, BB, CC) tests were conducted with all comparison stimuli visible from the beginning. The results suggest that the number of errors during transitivity, equivalence, and reflexivity tests progressively increased as participants were prevented from observing the correct comparison on a greater number of trials during training. Symmetry test results, however, were not affected by the experimental manipulation. Moreover, the number of participants showing reject-control patterns during tests slightly increased and the number of participants showing select-control patterns decreased as a function of the number of trials on which the participants were prevented from observing the correct comparison. Thus, we suggest that observing patterns during training is a relevant variable that affects equivalence test outcomes.     

Distance discrimination and observer strategy in judgments of relative size

Six paid Ss participated in an experiment designed to assess the effects of observer strategy and the detectability of a distance cue on judgments of relative size. Ss viewed stimulus pairs through a 21-in. tunnel at one end of an 8-ft table. The Standard stimulus, 94 in. from S, was individually paired with three larger and two smaller comparison stimuli 96 in. from S. A slit of light on the table 95 in. from S and 90 deg to his line of sight served as distance cue. Increases in distance detection improved accuracy of relative size judgments when the comparison stimulus was larger than the Standard stimulus, but decreased accuracy when the comparison stimulus was smaller. Magnitude of this effect varied directly with Ss’ post-experimental reports of judgmental strategy. These findings confirm the importance of distance discrimination in judgments of actual size and the necessity to control perceiver characteristics in the study of size-distance relationships.