Perceptual learning and perceptual search are altered in male university students with higher Autism Quotient scores

Two experiments investigated the validity of the Autism Quotient (AQ) scale for measuring traits associated with Autism Spectrum Disorders (ASD) in a population of male university students. Both studies found evidence that individuals who scored higher on the AQ questionnaire performed in a similar way to individuals with ASD on tasks with a perceptual component. Experiment 1 demonstrated a difference in the degree to which higher scoring AQ individuals performed on a perceptual learning task; with higher AQ scorers showing no advantage for familiar over novel items less. In Experiment 2, higher scorers showed fewer errors when judging the elements, as opposed to the global configuration, of a Navon task letter. Both of these patterns of results had previously been noted in individuals with ASD. These results suggest that the AQ may have some validity in identifying individuals in the nonclinical population with similar performance profiles to those with ASD.     

Perceptual learning in face processing: Comparison facilitates face recognition

Theoretical analyses of perceptual learning suggest that comparison between similar stimuli aids subsequent discrimination between them. The current studies examined whether the opportunity to compare a target face to other similar faces during a preexposure phase facilitated performance on a matching task. Performance was better when the target face had been presented in alternation with similar comparator faces than if that target had not been exposed before test. Exposure to the target face without comparators, or exposure alternating with dissimilar faces, improved performance relative to the nonexposed control but performance was not as good as when target exposure was given in alternation to similar comparison faces. The effects were not influenced by image changes between exposure and test. It is suggested that exposure to a face in comparison to similar stimuli focuses the central representation of a face on its unique features. In practical terms these results suggest that reliable identification of an individual from their photograph would be improved by viewing that photograph in comparison with photographs of similar people.     

Perceptual learning in flavor-aversion learning: Alternating and blocked exposure to a compound of flavors and to an element of that compound

Rats received different schedules of pre-exposure to a compound flavor (AX) and to one element of that compound (X). In Group ALT, exposure consisted of alternating trials with AX and X; Group BLK received a block with all AX trials before a separate block with all X trials (or vice versa). Discrimination between AX and X was assessed then by establishing an aversion to X and measuring the generalization of this aversion to AX. In Experiments 1A and 1B, generalization was less in Group ALT than in Group BLK. In Experiment 2, this latter result was confirmed and furthermore only Group ALT, and not Group BLK, showed less generalization than a group that received exposure to X alone. These results are discussed in terms of their implications for theories of perceptual learning.     

Perceptual learning effect on decision and confidence thresholds

Practice can enhance of perceptual sensitivity, a well-known phenomenon called perceptual learning. However, the effect of practice on subjective perception has received little attention. We approach this problem from a visual psychophysics and computational modeling perspective. In a sequence of visual search experiments, subjects significantly increased the ability to detect a “trained target”. Before and after training, subjects performed two psychophysical protocols that parametrically vary the visibility of the “trained target”: an attentional blink and a visual masking task. We found that confidence increased after learning only in the attentional blink task. Despite large differences in some observables and task settings, we identify common mechanisms for decision-making and confidence. Specifically, our behavioral results and computational model suggest that perceptual ability is independent of processing time, indicating that changes in early cortical representations are effective, and learning changes decision criteria to convey choice and confidence.     

The effect of statistical learning on internal stimulus representations: Predictable items are enhanced even when not predicted

Statistical learning is the automatic and unconscious learning of environmental regularities and is a basic mechanism of learning in a variety of human perceptual and cognitive domains. Previous studies have mainly focused on the associative mechanisms of statistical learning. However, an unexplored question is whether the internal representations of individual stimuli are altered as their associations are learned. Using a temporal statistical learning paradigm, we examine this question across three experiments and find clear evidence that the internal representations of individual stimuli are differentially altered according to their degree of temporal predictability. These findings complement previous accounts of statistical learning and reveal an enriched mechanism of human learning, such that learning to associate items also enhances the representations of certain items relative to others.     

Perceptual Learning

The extent of adult improvement in not only complex but also simple perceptual tasks is remarkable. Although this phenomenon has been noted and studied since the middle of the 19th century, recent advances in the study of brain physiology and anatomy afford new insights. Improvement specificity suggests that changes involve early sensory cortical areas, previously thought to lose their plasticity following the first years. The critical role of selective attention, even in learning the simplest tasks, as well as the precedence of learning easy cases, suggests the involvement of high-level cortical areas. Learning easy cases is more general than learning difficult cases. This pattern suggests the involvement of both high- and low-level areas in an orderly manner, with easy learning beginning at high-level areas and harder cases being resolved by access to low-level areas. The mapping of behavioral findings to underlying brain sites provides a unified framework for this interdisciplinary field.     

Perceptual adaptation to non-native speech

This study investigated talker-dependent and talker-independent perceptual adaptation to foreign-accent English. Experiment 1 investigated talker-dependent adaptation by comparing native English listeners' recognition accuracy for Chinese-accented English across single and multiple talker presentation conditions. Results showed that the native listeners adapted to the foreign-accented speech over the course of the single talker presentation condition with some variation in the rate and extent of this adaptation depending on the baseline sentence intelligibility of the foreign-accented talker. Experiment 2 investigated talker-independent perceptual adaptation to Chinese-accented English by exposing native English listeners to Chinese-accented English and then testing their perception of English produced by a novel Chinese-accented talker. Results showed that, if exposed to multiple talkers of Chinese-accented English during training, native English listeners could achieve talker-independent adaptation to Chinese-accented English. Taken together, these findings provide evidence for highly flexible speech perception processes that can adapt to speech that deviates substantially from the pronunciation norms in the native talker community along multiple acoustic-phonetic dimensions.     

The Influences of Category Learning on Perceptual Reconstructions

We explore different ways in which the human visual system can adapt for perceiving and categorizing the environment. There are various accounts of supervised (categorical) and unsupervised perceptual learning, and different perspectives on the functional relationship between perception and categorization. We suggest that common experimental designs are insufficient to differentiate between hypothesized perceptual learning mechanisms and reveal their possible interplay. We propose a relatively underutilized way of studying potential categorical effects on perception, and we test the predictions of different perceptual learning models using a two-dimensional, interleaved categorization-plus-reconstruction task. We find evidence that the human visual system adapts its encodings to the feature structure of the environment, uses categorical expectations for robust reconstruction, allocates encoding resources with respect to categorization utility, and adapts to prevent miscategorizations.     

Visual learning of statistical relations among nonadjacent features: Evidence for structural encoding

Recent results suggest that observers can learn, unsupervised, the co-occurrence of independent shape features in viewed patterns (e.g., Fiser & Aslin, 2001). A critical question with regard to these findings is whether learning is driven by a structural, rule-based encoding of spatial relations between distinct features or by a pictorial, template-like encoding, in which spatial configurations of features are embedded in a “holistic” fashion. In two experiments, we test whether observers can learn combinations of features when the paired features are separated by an intervening spatial “gap”, in which other, unrelated features can appear. This manipulation both increases task difficulty and makes it less likely that the feature combinations are encoded simply as larger unitary features. Observers exhibited learning consistent with earlier studies, suggesting that unsupervised learning of compositional structure is based on the explicit encoding of spatial relations between separable visual features. More generally, these results provide support for compositional structure in visual representation.     

On the automaticity of pure perceptual sequence learning

We investigated the automaticity of implicit sequence learning by varying perceptual load in a pure perceptual sequence learning paradigm. Participants responded to the randomly changing identity of a target, while the irrelevant target location was structured. In Experiment 1, the target was presented under low or high perceptual load during training, whereas testing occurred without load. Unexpectedly, no sequence learning was observed. In Experiment 2, perceptual load was introduced during the test phase to determine whether load is required to express perceptual knowledge. Learning itself was unaffected by visuospatial demands, but more learning was expressed under high load test conditions. In Experiment 3, we demonstrated that perceptual load is not required for the acquisition of perceptual sequence knowledge. These findings suggest that perceptual load does not mediate the perceptual sequence learning process itself, supporting the automaticity of implicit learning, but is mandatory for the expression of pure perceptual sequence knowledge.     

Unconscious reward facilitates motion perceptual learning

Reward signal plays an important role in guiding human learning behaviour. Recent studies have provided evidence that reward signal modulates perceptual learning of basic visual features. Typically, the reward effects on perceptual learning were accompanied with consciously presented reward during the learning process. However, whether an unconsciously presented reward signal that minimizes the contribution of attentional and motivational factors can facilitate perceptual learning remains less well understood. We trained human subjects on a visual motion detection task and subliminally delivered a monetary reward for correct response during the training. The results showed significantly larger learning effect for high reward-associated motion direction than low reward-associated motion direction. Importantly, subjects could neither discriminate the relative values of the subliminal monetary reward nor correctly report the reward-direction contingencies. Our findings suggest that reward signal plays an important modulatory role in perceptual learning even if the magnitude of the reward was not consciously perceived.     

Perceptual constraints and the learnability of simple grammars

Cognitive processes are often attributed to statistical or symbolic general-purpose mechanisms. Here we show that some spontaneous generalizations are driven by specialized, highly constrained symbolic operations. We explore how two types of artificial grammars are acquired, one based on repetitions and the other on characteristic relations between tones ("ordinal" grammars). Whereas participants readily acquire repetition-based grammars, displaying early electrophysiological responses to grammar violations, they perform poorly with ordinal grammars, displaying no such electrophysiological responses. This outcome is problematic for both general symbolic and statistical models, which predict that both types of grammars should be processed equally easily. This suggests that some simple grammars are acquired using perceptual primitives rather than general-purpose mechanisms; such primitives may be elements of a "toolbox" of specialized computational heuristics, which may ultimately allow constructing a psychological theory of symbol manipulation.     

Memory encoding of stimulus features in human perceptual learning

Two experiments analysed memory encoding in human perceptual learning. Both experiments started with preexposure without feedback to four checkerboards composed by a unique feature each and sharing a common feature (AX, BX, CX, and DX). Elements of one pair were presented intermixed and elements of the other pair were presented in separate blocks. Immediately after preexposure participants completed a memory recognition task in which the characteristics of the distractors were manipulated. Experiment 1 showed that only intermixed presentation results in good encoding of the unique features of the stimuli. Experiment 2 demonstrated that intermixed preexposure results in different encoding of unique versus common features of the stimuli: Participants are able to remember A and B better than they remember X, whereas for the blocked condition memory for C, D, and X does not differ. Overall, the results presented here support the proposal that intermixing stimuli results in differential memory traces for unique versus common features and that this contributes to the intermixed/blocked effect.     

Social cues modulate the representations underlying cross-situational learning

Because children hear language in environments that contain many things to talk about, learning the meaning of even the simplest word requires making inferences under uncertainty. A cross-situational statistical learner can aggregate across naming events to form stable word-referent mappings, but this approach neglects an important source of information that can reduce referential uncertainty: social cues from speakers (e.g., eye gaze). In four large-scale experiments with adults, we tested the effects of varying referential uncertainty in cross-situational word learning using social cues. Social cues shifted learners away from tracking multiple hypotheses and towards storing only a single hypothesis (Experiments 1 and 2). In addition, learners were sensitive to graded changes in the strength of a social cue, and when it became less reliable, they were more likely to store multiple hypotheses (Experiment 3). Finally, learners stored fewer word-referent mappings in the presence of a social cue even when given the opportunity to visually inspect the objects for the same amount of time (Experiment 4). Taken together, our data suggest that the representations underlying cross-situational word learning of concrete object labels are quite flexible: In conditions of greater uncertainty, learners store a broader range of information.     

Perceptual training strongly improves visual motion perception in schizophrenia

Schizophrenia patients exhibit perceptual and cognitive deficits, including in visual motion processing. Given that cognitive systems depend upon perceptual inputs, improving patients’ perceptual abilities may be an effective means of cognitive intervention. In healthy people, motion perception can be enhanced through perceptual learning, but it is unknown whether this perceptual plasticity remains in schizophrenia patients. The present study examined the degree to which patients’ performance on visual motion discrimination can be improved, using a perceptual learning procedure. While both schizophrenia patients and healthy controls showed decreased direction discrimination thresholds (improved performance) with training, the magnitude of the improvement was greater in patients (47% improvement) than in controls (21% improvement). Both groups also improved moderately but non-significantly on an untrained task—speed discrimination. The large perceptual training effect in patients on the trained task suggests that perceptual plasticity is robust in schizophrenia and can be applied to develop bottom-up behavioral interventions.     

Developing PFC representations using reinforcement learning

From both functional and biological considerations, it is widely believed that action production, planning, and goal-oriented behaviors supported by the frontal cortex are organized hierarchically [Fuster (1991); Koechlin, E., Ody, C., & Kouneiher, F. (2003). Neuroscience: The architecture of cognitive control in the human prefrontal cortex. Science, 424, 1181-1184; Miller, G. A., Galanter, E., & Pribram, K. H. (1960). Plans and the structure of behavior. New York: Holt]. However, the nature of the different levels of the hierarchy remains unclear, and little attention has been paid to the origins of such a hierarchy. We address these issues through biologically-inspired computational models that develop representations through reinforcement learning. We explore several different factors in these models that might plausibly give rise to a hierarchical organization of representations within the PFC, including an initial connectivity hierarchy within PFC, a hierarchical set of connections between PFC and subcortical structures controlling it, and differential synaptic plasticity schedules. Simulation results indicate that architectural constraints contribute to the segregation of different types of representations, and that this segregation facilitates learning. These findings are consistent with the idea that there is a functional hierarchy in PFC, as captured in our earlier computational models of PFC function and a growing body of empirical data.     

Perceptual learning for speech

Adult language users have an enormous amount of experience with speech in their native language. As a result, they have very well-developed processes for categorizing the sounds of speech that they hear. Despite this very high level of experience, recent research has shown that listeners are capable of redeveloping their speech categorization to bring it into alignment with new variation in their speech input. This reorganization of phonetic space is a type of perceptual learning, or recalibration, of speech processes. In this article, we review several recent lines of research on perceptual learning for speech.     

Visual statistical learning in infancy: evidence for a domain general learning mechanism

The rapidity with which infants come to understand language and events in their surroundings has prompted speculation concerning innate knowledge structures that guide language acquisition and object knowledge. Recently, however, evidence has emerged that by 8 months, infants can extract statistical patterns in auditory input that are based on transitional probabilities defining the sequencing of the input's components (Science 274 (1996) 1926). This finding suggests powerful learning mechanisms that are functional in infancy, and raises questions about the domain generality of such mechanisms. We habituated 2-, 5-, and 8-month-old infants to sequences of discrete visual stimuli whose ordering followed a statistically predictable pattern. The infants subsequently viewed the familiar pattern alternating with a novel sequence of identical stimulus components, and exhibited significantly greater interest in the novel sequence at all ages. These results provide support for the likelihood of domain general statistical learning in infancy, and imply that mechanisms designed to detect structure inherent in the environment may play an important role in cognitive development.     

Perceptual Learning of Intonation Contour Categories in Adults and 9‐ to 11‐Year‐Old Children: Adults Are More Narrow‐Minded

We report on rapid perceptual learning of intonation contour categories in adults and 9‐ to 11‐year‐old children. Intonation contours are temporally extended patterns, whose perception requires temporal integration and therefore poses significant working memory challenges. Both children and adults form relatively abstract representations of intonation contours: Previously encountered and novel exemplars are categorized together equally often, as long as distance from the prototype is controlled. However, age‐related differences in categorization performance also exist. Given the same experience, adults form narrower categories than children. In addition, adults pay more attention to the end of the contour, while children appear to pay equal attention to the beginning and the end. The age range we examine appears to capture the tail‐end of the developmental trajectory for learning intonation contour categories: There is a continuous effect of age on category breadth within the child group, but the oldest children (older than 10;3) are adult‐like.     

Perceptual hysteresis as a marker of perceptual inflexibility in schizophrenia

People with schizophrenia are known to exhibit difficulties in the updating of their current belief states even in the light of disconfirmatory evidence. In the present study we tested the hypothesis that people with schizophrenia could also manifest perceptual inflexibility, or difficulties in the updating of their current sensory states. The presence of perceptual inflexibility might contribute both to the patients’ altered perception of reality and the formation of some delusions as well as to their social cognition deficits. Here, we addressed this issue with a protocol of auditory hysteresis, a direct measure of sensory persistence, on a population of stabilized antipsychotic-treated schizophrenia patients and a sample of control subjects. Trials consisted of emotional signals (i.e., screams) and neutral signals (i.e., spectrally-rotated versions of the emotional stimuli) progressively emerging from white noise – Ascending Sequences – or progressively fading away in white noise – Descending Sequences. Results showed that patients presented significantly stronger hysteresis effects than control subjects, as evidenced by a higher rate of perceptual reports in Descending Sequences. The present study thus provides direct evidence of perceptual inflexibility in schizophrenia.