Learning efficient visual search for stimuli containing diagnostic spatial configurations and color-shape conjunctions

Visual search is often slow and difficult for complex stimuli such as feature conjunctions. Search efficiency, however, can improve with training. Search for stimuli that can be identified by the spatial configuration of two elements (e.g., the relative position of two colored shapes) improves dramatically within a few hundred trials of practice. Several recent imaging studies have identified neural correlates of this learning, but it remains unclear what stimulus properties participants learn to use to search efficiently. Influential models, such as reverse hierarchy theory, propose two major possibilities: learning to use information contained in low-level image statistics (e.g., single features at particular retinotopic locations) or in high-level characteristics (e.g., feature conjunctions) of the task-relevant stimuli. In a series of experiments, we tested these two hypotheses, which make different predictions about the effect of various stimulus manipulations after training. We find relatively small effects of manipulating low-level properties of the stimuli (e.g., changing their retinotopic location) and some conjunctive properties (e.g., color-position), whereas the effects of manipulating other conjunctive properties (e.g., color-shape) are larger. Overall, the findings suggest conjunction learning involving such stimuli might be an emergent phenomenon that reflects multiple different learning processes, each of which capitalizes on different types of information contained in the stimuli. We also show that both targets and distractors are learned, and that reversing learned target and distractor identities impairs performance. This suggests that participants do not merely learn to discriminate target and distractor stimuli, they also learn stimulus identity mappings that contribute to performance improvements.     

Resources required for processing ambiguous complex features in vision and audition are modality specific

Processing multiple complex features to create cohesive representations of objects is an essential aspect of both the visual and auditory systems. It is currently unclear whether these processes are entirely modality specific or whether there are amodal processes that contribute to complex object processing in both vision and audition. We investigated this using a dual-stream target detection task in which two concurrent streams of novel visual or auditory stimuli were presented. We manipulated the degree to which each stream taxed processing conjunctions of complex features. In two experiments, we found that concurrent visual tasks that both taxed conjunctive processing strongly interfered with each other but that concurrent auditory and visual tasks that both taxed conjunctive processing did not. These results suggest that resources for processing conjunctions of complex features within vision and audition are modality specific.     

The Hemispheric Lateralization for Processing Geometric Word/Shape Combinations: The Stroop-Shape Effect

The authors conducted 4 experiments to test whether hemispheric lateralization occurs for the processing of geometric word–shape combinations. In 3 experiments, participants responded to geometric shapes combined with geometric words (square, circle, triangle). In the 4th experiment, stimuli were combinations of geometric shapes and nongeometric words. The authors predicted that it would take longer to respond in incongruent conditions (e.g., the word “square” combined with the shape of a circle) than in congruent conditions. The authors found the strongest incongruency effects for the dominant hemisphere—that is, the left hemisphere for responding to words and the right hemisphere for responding to shapes. A Shape Interfering Properties hypothesis (SIP) is a possible explanation for these results.     

Cognitive changes in conjunctive rule-based category learning: An ERP approach

When learning rule-based categories, sufficient cognitive resources are needed to test hypotheses, maintain the currently active rule in working memory, update rules after feedback, and to select a new rule if necessary. Prior research has demonstrated that conjunctive rules are more complex than unidimensional rules and place greater demands on executive functions like working memory. In our study, event-related potentials (ERPs) were recorded while participants performed a conjunctive rule-based category learning task with trial-by-trial feedback. In line with prior research, correct categorization responses resulted in a larger stimulus-locked late positive complex compared to incorrect responses, possibly indexing the updating of rule information in memory. Incorrect trials elicited a pronounced feedback-locked P300 elicited which suggested a disconnect between perception, and the rule-based strategy. We also examined the differential processing of stimuli that were able to be correctly classified by the suboptimal single-dimensional rule (“easy” stimuli) versus those that could only be correctly classified by the optimal, conjunctive rule (“difficult” stimuli). Among strong learners, a larger, late positive slow wave emerged for difficult compared with easy stimuli, suggesting differential processing of category items even though strong learners performed well on the conjunctive category set. Overall, the findings suggest that ERP combined with computational modelling can be used to better understand the cognitive processes involved in rule-based category learning.     

Conditionals and conditional probability

The authors report 3 experiments in which participants were invited to judge the probability of statements of the form if p then q given frequency information about the cases pq, p not q, not pq, and not p not q (where not = not). Three hypotheses were compared: (a) that people equate the probability with that of the material conditional, 1 - P(p not q); (b) that people assign the conditional probability, P(q/p); and (c) that people assign the conjunctive probability P(pq). The experimental evidence allowed rejection of the 1st hypothesis but provided some support for the 2nd and 3rd hypotheses. Individual difference analyses showed that half of the participants used conditional probability and that most of the remaining participants used conjunctive probability as the basis of their judgments.     

Response selection processes for conjunctive targets

A model is proposed for identification and response selection of cross-dimensional conjunctive stimuli. The model assumes that the formation of conjunction representations involves processes similar to those used in response selection for single-feature targets. It predicts that discrimination between conjunctive targets leads to separate competitions in each of the relevant component dimensions and that detection of a predefined single conjunctive target is done at the conjunctive map level. Experiments 1 and 2 support these two sets of predictions. Experiment 3 demonstrates that responses to conjunctions of features within the orientation dimension are qualitatively different from those for cross-dimensional conjunctive targets. It is speculated that line-orientation conjunctions are handled by the visual object-recognition system, whereas cross-dimensional conjunctions, as exemplified by the model, may be performed by a different system that is closely associated with response selection processes.     

Prototypes are attractive because they are easy on the mind

People tend to prefer highly prototypical stimuli--a phenomenon referred to as the beauty-in-averageness effect. A common explanation of this effect proposes that prototypicality signals mate value. Here we present three experiments testing whether prototypicality preference results from more general mechanisms-fluent processing of prototypes and preference for fluently processed stimuli. In two experiments, participants categorized and rated the attractiveness of random-dot patterns (Experiment 1) or common geometric patterns (Experiment 2) that varied in levels of prototypicality. In both experiments, prototypicality was a predictor of both fluency (categorization speed) and attractiveness. Critically, fluency mediated the effect of prototypicality on attractiveness, although some effect of prototypicality remained when fluency was controlled. The findings were the same whether or not participants explicitly considered the pattern's categorical membership, and whether or not categorization fluency was salient when they rated attractiveness. Experiment 3, using the psychophysiological technique of facial electromyography, confirmed that viewing abstract prototypes elicits quick positive affective reactions.     

Instructional control of generalized relational matching to sample in children.

Three experiments examined the performance of 4-year-old children in matching geometric stimuli. Performance was developed as a simulation in which all components of the behavior were overt and directly measured. A correct match depended on the state of an instructional stimulus: the background color of the display. In the first two experiments, on nonidentity trials (signified by a green background) the next longer length, larger size, or greater distance was correct. With a blue background, a comparison identical to the sample was correct. In Experiment 3, red was added for which shorter, smaller, or nearer was correct. Also here, on nonidentity trials, if a comparison of the correct length was not presented, the children adjusted their search target to the comparison of the next succeeding size (larger or smaller) so as to maintain a constant matching relation. Subsequently, when exposure to the instructional stimulus was reduced to presentation only at the beginning of each trial, performance simulated matching based on instructions about abstract relations. In all experiments, accurate matching generalized across novel stimuli and reduced exposure to the instructional stimuli.     

The perceptual origins of the abstract same/different concept in human infants

Very few experiments have studied the two item same/different relation in young human infants. This contrasts with an extensive animal literature. We tested young infants with two novel tasks designed specifically to provide convergent comparative measures. Each infant completed both tasks allowing an assessment of their understanding of the abstract concept rather than task-specific abilities. In a looking time task with photographic stimuli, we found that 8-month-olds are sensitive to the relation but 4-month-olds are not. The second task used an anticipatory eye movement paradigm with simple geometric stimuli. On each trial, two colored shapes appear and moved upwards behind an occluder. They reappeared on either the upper left or right depending on the relation between them. Infants at both ages learned and generalized the dependency but only for the different relation. These results show that human infants can learn the same/different concept but that, in strong continuity with animal results, their abilities are firmly grounded in perception.     

Mental representation and hypothetico-deductive reasoning: The case of the THOG problem

Summary This article reports three experiments that deal with the source of the difficulty of Wason's (1977) THOG problem. The solution of this problem demands both the postulation of hypotheses and a combinatorial analysis of their consequences. Experiment 1 showed that the generation of the hypotheses is not in itself sufficient to solve the problem. Experiment 2 showed that a version presenting a plausible context for separating the level of data from that of hypotheses produced a better performance than both the original abstract version and a thematic version lacking the plausible context separating the levels. Experiment 3 gave evidence that this context can produce facilitation even with the geometric material of the classic version. This experiment also showed that a pictorial presentation of data and a verbal presentation of hypotheses affect performance negatively. The results demonstrate the role of problem representation in problem solving, and, in particular, the role of homogeneity in representing data and hypotheses in hypothetico-deductive reasoning.     

Unitization during category learning

Five experiments explored the question of whether new perceptual units can be developed if they are useful for a category learning task, and if so, what the constraints on this unitization process are. During category learning, participants were required to attend either a single component or a conjunction of 5 components. Consistent with unitization, the conjunctive task became much easier with practice; this improvement was not found for the single-component task or for conjunctive tasks in which the components could not be unitized. Influences of component organization (Experiment 1), component contiguity (Experiment 2), component proximity (Experiment 3), and number of components (Experiment 4) on practice effects were found. Deconvolved response times (Experiment 5) showed that prolonged practice yielded faster responses than predicted by an analytic model that integrates evidence from independently perceived components.     

Visual evoked potentials elicited by subjective contour figures

In order to investigate the relationship between the appearance of illusory figures and the wave form of visual evoked potentials (VEPs), 8 different visual pattern stimuli were presented to 8 normal subjects. Four of the stimuli (experimental stimuli) produced subjective figures and contours (squares and discs). The 4 other stimuli (reference stimuli), although equal to the experimental stimuli in the amount of physical energy, did not produce the illusion of squares or discs. Electrodes were placed on the scalp at central and occipital locations. Three prominent peaks in the occipital record were observed in all subjects. An amplitude difference of VEP N180 (N2) between the subjective figures and the reference stimuli was found in the values for each subject. Enhancement of the VEP of the illusory figure stimuli was observed for a specific component (N2), whereas the amplitude values at the central components and the occipital P120 (P2) and P280 (P3) were almost the same as the reference values. The VEP (N2 component) amplitude enhancement at the occipital area for subjective figure stimuli suggests that illusory contour formation takes place at higher levels in the visual system. This was known from experiments using dichoptic presentation.     

Recall and recognition hypermnesia for Socratic stimuli

In two experiments, we investigate hypermnesia, net memory improvements with repeated testing of the same material after a single study trial. In the first experiment, we found hypermnesia across three trials for the recall of word solutions to Socratic stimuli (dictionary-like definitions of concepts) replicating Erdelyi, Buschke, and Finkelstein and, for the first time using these materials, for their recognition. In the second experiment, we had two “yes/no” recognition groups, a Socratic stimuli group presented with concrete and abstract verbal materials and a word-only control group. Using signal detection measures, we found hypermnesia for concrete Socratic stimuli—and stable performance for abstract stimuli across three recognition tests. The control group showed memory decrements across tests. We interpret these findings with the alternative retrieval pathways (ARP) hypothesis, contrasting it with alternative theories of hypermnesia, such as depth of processing, generation and retrieve–recognise. We conclude that recognition hypermnesia for concrete Socratic stimuli is a reliable phenomenon, which we found in two experiments involving both forced-choice and yes/no recognition procedures.     

On the relation between time and space in the visual discrimination of velocity.

Is the perception of velocity determined by the prior discrimination of spatial and temporal distances? Two experiments sought to answer this question by comparing the discriminabilities of moving stimuli varied in spatial extent, temporal duration, or in redundant combinations of both variables. The subject's task was to identify which of two alternative stimuli was presented on each trial. A set of four stimuli was constructed from two values of spatial extent and two values of temporal duration. Separate conditions required discrimination of each of the six possible pairs of these stimuli. Experiment 1 examined continuous motion and Experiment 2 examined apparent motion for stimuli with short (50 versus 65 msec) and with long (500 versus 650 msec) interstimulus intervals. With continuous motion and with good apparent motion (short intervals), the discrimination between the different-velocity bivariate pairs was too accurate to be attributed only to discriminations of the spatial and temporal extents of the motion. This did not occur with poor apparent motion. Evidently, time and space are perceptually related.     

Classification of exemplars with single- and multiple-feature manifestations: the effects of relevant dimension variation and category structure

Most classification research focuses on cases in which each abstract feature has the same surface manifestation whenever it is presented. Previous research finds that people have difficulty learning to classify when each abstract feature has multiple surface manifestations. These studies created multiple manifestations by varying aspects of the stimuli irrelevant to the abstract feature dimension. In this article, multiple manifestations were created by varying aspects of the stimuli relevant to the abstract feature dimension. People given categories with the family resemblance category structure often used in psychology experiments had difficulty learning to classify when multiple manifestations were present, even though the variation was relevant. This effect was reversed when a family resemblance structure with nondiagnostic values was used.     

Typicality effects in contingency-shaped generalized equivalence classes

Two experiments were conducted using match-to-sample methodologies in an effort to model lexical classes, which include both arbitrary and perceptual relations between class members. Training in both experiments used a one-to-many mapping procedure with nonsense syllables as samples and eight sets of abstract stimuli as comparisons. These abstract stimuli differed along a number of dimensions, four of which were critical to the experimenter-defined class membership. Stimuli in some comparison sets included only one of the class-defining features, but stimuli in other sets included two, three, or all four of the critical features. After mastery of the baseline training, three types of probe tests were conducted: symmetry, transitivity/equivalence, and novel probe tests in which the training nonsense syllables served as samples, and comparisons were novel abstract stimuli that included one or more of the class-defining features. Symmetry and transitivity/equivalence probe tests showed that the stimuli used in training became members of equivalence classes. The novel stimuli also became class members on the basis of inclusion of any of the critical features. Thus these probe tests revealed the formation of open-ended generalized equivalence classes. In addition, typicality effects were observed such that comparison sets with more critical features were learned with fewer errors, responded to more rapidly, and judged to be better exemplars of the class. Contingency-shaped stimulus classes established through a match-to-sample procedure thus show several important behavioral similarities to natural lexical categories.     

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.     

Psychological analyses of haptic and haptic-visual judgements of extent

Magnitude estimates of haptic extent resulted in positively accelerated psychophysical power function with an exponent of 1.18. However, in two further experiments right-handed male subjects made rating-scale judgements of the combined width of two stimulus blocks. Six widths were used and five replications of the 36 factorial combinations were presented to each subject. In Experiment II both stimuli were out of view and one was held between the thumb and index finger of each hand. In Experiment III one stimulus was held out of view between thumb and finger of the right hand and the second was shown to the subject. Mean ratings in both experiments were fit by a model which assumes that responses are a weighted average of the scale values of the two stimuli (Anderson, 1974a).     

Relative judgments affect assessments of stimulus duration

Humans were trained on two independent temporal discriminations, with correct choice dependent on the initial stimulus duration. In Experiment 1, the durations were 1.0 and 4.0 sec, with one set of choice stimuli, and 2.0 and 8.0 sec, with a different set of choice stimuli. The 2.0- and 4.0-sec values were selected to be the geometric mean of the two values in the other discrimination. In Experiment 2, the durations were 2.0 and 5.0 sec for one discrimination and 3.5 and 6.5 sec for the other. The 3.5- and 5.0-sec values were selected to be the arithmetic mean of the two values in the other discrimination. In both experiments, participants showed evidence for relational coding of the duration pairs. That is, the test durations were selected to be at the presumed bisection point (i.e., they should have produced indifferent choice), but instead the shorter test duration from the longer duration pair produced a “short” bias (in both experiments), whereas the longer duration from the shorter duration pair produced a “long” bias (in the second experiment). Results were similar to those from Zentall, Weaver, and Clement (2004) with pigeons.     

Abstraction of prototypical information by adults and 10-month-old infants

The primary purpose of this study was to investigate whether preverbal infants, when presented with exemplars of an artificially constructed category, would abstract a prototypical representation of the category, and if so, whether this representation was formed by either "counting" or "averaging" the features that were varying among category members. Two experiments are reported. In Experiment 1, a set of stimuli was developed and tested for which it was demonstrated that adult subjects would readily abstruct either a modal or an average prototypical representation. The type of representation abstracted was found to be dependent on the discriminability of the feature values. In Experiment 2, 10-mo.-old infants were tested using a habituation paradigm with the stimuli developed in the first experiment. The results of this study indicated that the infants were also able to abstract the featural information that was varying among the exemplars of the category, and the infants formed an internal represenatation of the category by averaging feature values. Thus, the results clearly imply that infants are able to constructively process visual information and hence take a more active role in category formation than had been previously believed.