Simultaneous presentation of similar stimuli produces perceptual learning in human picture processing.

Human participants received unsupervised exposure to difficult-to-discriminate stimuli (e.g., A and A′), created with a morphing procedure from photographs of faces, before learning a discrimination between them. Experiments 1 and 2 demonstrated that prior exposure enhanced later discrimination and that intermixed exposure (A, A′, A, A′...) resulted in better subsequent discrimination than blocked exposure (B, B, ...B′, B′...). Experiments 3 and 4 showed that simultaneous exposure to 2 similar stimuli facilitated the later acquisition of both a simultaneous and a successive discrimination, and this effect was observed even though simultaneous exposure to 2 stimuli fostered the development of an excitatory association between them (Experiment 5). The findings of Experiments 1 and 2 revealed a perceptual learning effect with pictures of faces, and the findings of Experiments 3-5 are difficult to reconcile with associative analyses of perceptual learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Enhanced discrimination between flavor stimuli: Roles of salience modulation and inhibition.

Rats were given intermixed preexposure to the compound flavors AX and BX and to the compound CX in a separate block of trials (4 presentations of each compound). In Experiment 1, rats showed less generalization of conditioned aversion from AX to BX than from CX to BX, a perceptual learning effect. Experiment 2 showed that the formation of an excitatory association proceeded more readily between A and B than between C and B, suggesting that intermixed preexposure maintains the effective salience of A and B and does not establish inhibition between them, a process that would require prolonged preexposure. According to this analysis, salience modulation and associative inhibition may contribute to perceptual learning at different stages of preexposure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of the role of associative inhibition in perceptual learning by means of the same-different task.

In Experiment 1a, participants were exposed, over a series of trials, to separate presentations of 2 similar checkerboard stimuli, AX and BX (where X represents a common background). In one group, AX and BX were presented on alternating trials (intermixed), in another, they were presented in separate blocks of trials (blocked). The intermixed group performed to a higher standard than the blocked group on a same-different test. A superiority of intermixed over blocked exposure was also evident in a within-subject design (Experiment 1b) and when the test required discrimination between a preexposed stimulus and the background (e.g., AX vs. X), even if the background changed between preexposure and test (AY vs. Y) (Experiment 2). In Experiment 3, the intermixed/blocked effect was observed when, in preexposure, stimulus presentations were alternated with the background alone (e.g., AX/X). This suggests that the perceptual learning effect is not the consequence of inhibitory associations between unique features but to increased salience of those features. Experiment 4 confirmed this finding and also ruled out an account of the effect in terms of trial spacing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative activation of stimulus representations restores lost salience: Implications for perceptual learning.

In 3 experiments, rats received preexposure to presentations of a compound flavor BX. The effective salience of B was then tested by assessing its ability to interfere with the aversion controlled by another flavor or the tendency to drink a saline solution after the induction of a salt need. It was found that the effective salience of B was maintained when during preexposure, presentations of BX alternated with presentations of X alone. This was true both when BX was presented as a simultaneous compound (Experiment 1) and as a serial compound (X→B; Experiments 2 and 3); salience was not maintained when the serial compound took the form B→X (Experiments 2 and 3a). It was argued that the salience of B declines during preexposure but is restored when presentations of X are able to activate the representation of B by way of the associative X-B link. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attention and relative novelty in human perceptual learning.

Four experiments examined the role of attention in human perceptual learning. In Experiment 1, participants were preexposed to a pair of visual (checkerboard) stimuli AX and BX, with common elements X and unique features A and B. A same-different task was then used to assess discrimination of AX and BX and a pair of control stimuli, CY and DY. In addition, participants' eye movements were recorded to assess the role of attentional processes. The results showed that preexposure enhanced discrimination between AX and BX. Furthermore, participants showed greater attention to the preexposed unique features A and B than to the novel unique features C and D, as measured by the eye gaze monitor. Experiments 2 and 3 examined the prediction that perceptual learning is due to the relative familiarity of the common and unique stimulus features. Experiment 4 replicated the intermixed-blocked effect and showed that the way in which AX and BX are presented is also important for perceptual learning. The results generally support the idea that intermixed preexposure to AX and BX increases attention to the unique stimulus features A and B. Some aspects of the results are consistent with a relative novelty account, whereas others implicate a high-level attentional process that is not driven by stimulus novelty. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The intermixed-blocked effect in human perceptual learning is not the consequence of trial spacing.

A robust finding in humans and animals is that intermixed exposure to 2 similar stimuli (AX/BX) results in better discriminability of those stimuli on test than does exposure to 2 equally similar stimuli in 2 separate blocks (CX_DX)--the intermixed-blocked effect. This intermixed-blocked effect may be an example of the superiority of spaced over massed practice; in the intermixed, but not the blocked exposure regime, each presentation of a given stimulus (e.g., AX) is separated from the next by the presentation of its partner (BX). Two experiments with human participants replicated the intermixed-blocked effect and showed that the effect was not due to the spacing of exposure trials. A mechanism for the intermixed-blocked effect is proposed, which combines theories from associative learning and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhibitory associations contribute to perceptual learning in humans.

Perceptual learning in humans was examined in 2 experiments. In Experiment 1, participants received intermixed exposure to 2 similar compounds (AX, BX, AX, BX, . . .) and blocked exposure to a 2nd pair of similar compounds (CY, CY, . . . , DY, DY, . . .). Aversions established to AX and CY generalized less to BX than to DY. In Experiment 2, 1 pair of compounds was presented in a forward order (i.e., AX3BX), whereas the 2nd pair of compounds was presented in a backward order (i.e., DY→CY). Aversions established to AX and CY generalized less to BX than to DY. These results indicate that inhibitory associations contribute to perceptual learning in humans and thereby establish a fundamental similarity between the mechanisms that underlie perceptual learning in humans and rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Avoidance learning of perceptual defense and vigilance.

Thirty-two undergraduates were randomly assigned to defense and vigilance training groups. "This study supports the view that perceptual defense and vigilance are learned reactions to anxiety arousing stimuli." A behavior theory analysis of the learning process is proposed. "According to this analysis, perceptual defense is learned when the perceptual response to a threatening stimulus is punished and competing perceptual responses are instrumental to anxiety reduction. Competing perceptual responses when reinforced are strengthened at the expense of the critical perceptual response. Perceptual vigilance is learned when the perceptual response to a threatening stimulus is reinforced by anxiety reduction and competing perceptual responses are punished." Learning for both groups "proceeded in the absence of awareness." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequence effects in categorization of simple perceptual stimuli.

Categorization research typically assumes that the cognitive system has access to a (more or less noisy) representation of the absolute magnitudes of the properties of stimuli and that this information is used in reaching a categorization decision. However, research on identification of simple perceptual stimuli suggests that people have very poor representations of absolute magnitude information and that judgments about absolute magnitude are strongly influenced by preceding material. The experiments presented here investigate such sequence effects in categorization tasks. Strong sequence effects were found. Classification of a borderline stimulus was more accurate when preceded by a distant member of the opposite category than by a distant member of the same category. It is argued that this category contrast effect cannot be accounted for by extant exemplar or decision-bound models of categorization. The effect suggests the use of relative magnitude information in categorization. A memory and contrast model illustrates how relative magnitude information may be used in categorization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preexposure effects in the spatial domain: Dissociation between latent inhibition and perceptual learning.

In 4 experiments, rats were given intermixed or blocked preexposure to an array of landmarks that subsequently defined the location of a hidden goal in a Morris pool task. Previous research has shown that intermixed preexposure to pairs of adjacent landmarks retards learning whereas preexposure to individual landmarks facilitates subsequent learning (J. Prados, V. D. Chamizo, & N. J. Mackintosh, 1999). Accordingly, in Experiment 1, intermixed and blocked preexposure to pairs of adjacent landmarks was found to retard learning. In Experiment 2, however, a scheduling effect was found: Rats given intermixed preexposure to the individual landmarks learned faster than rats given blocked or no preexposure. Experiment 3 showed that intermixed (but not blocked) preexposure to pairs of landmarks resulted in a facilitatory effect when preexposure and test were carried out in different contexts. Experiment 4 replicated within a single experiment the main results observed in Experiments 1 and 3. This pattern of results suggests that intermixed preexposure engages learning processes other than latent inhibition that facilitate subsequent learning of the navigation task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory predictions are influenced by perceptual information: Evidence for metacognitive illusions.

Although perceptual information is utilized to judge size or depth, little work has investigated whether such information is used to make memory predictions. The present study examined how the font size of to-be-remembered words influences predicted memory performance. Participants studied words for a free-recall test that varied in font size and made judgments of learning (JOLs) for each item. JOLs were influenced by font size, as larger font sizes were given higher JOLs, whereas little relationship was evident between font size and recall. The effect was modified when other, more valid, sources of information (e.g., associative strength) were available when JOLs were made and persisted despite experience with multiple study-test sessions, use of a forgetting scale to assess predictions, and explicit warning of participants that font size has little effect on memory performance. When ease of reading was manipulated, such that large font size words were made less fluent, the effect was eliminated. Thus, highly accessible perceptual cues can strongly influence JOLs, likely via encoding fluency, and this effect can lead to metacognitive illusions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contributions of procedure and stimulus learning to early, rapid perceptual improvements.

Improvements in performance on many perceptual skills can occur with only a single training session. Of interest here is what aspects of the training experience are being learned during this brief exposure. Although there is considerable evidence that learning associated with specific feature values of the stimulus used in training (stimulus learning) contributes to these rapid improvements, there has been little direct investigation of the possibility that other types of learning do so as well. Here the authors show that not only stimulus learning but also learning of more general aspects of the training experience (procedure learning) contributed to rapid improvements in performance on interaural time difference discrimination. However, practice on the type of judgment to be made did not appear to aid performance (no task learning). These results are consistent with physiological reports that different neural mechanisms are engaged at different time points during even a brief training session, and imply that the circuits that are engaged and likely modified vary in the degree of their selectivity to the target condition. Such changes presumably enable further learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination learning set in Rhesus monkeys.

The rate of acquisition of discrimination learning set in rhesus monkeys is related to amount of within-problem learning difficulty, and amount of separation between stimuli and respones loci. Experimentally naive monkeys have a weak tendency to approach novel stimuli, but because of generalization from the positive to the negative stimulus within a problem, experimentally sophisticated monkeys tend to approach familiar negative stimuli rather than new stimuli. Early in training there are more errors following a first-trial error than following a correct first-trial response, but later this trend is reversed. All of the data can be accounted for by Hull-Spence theory, with a small number of assumptions added. (79 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recency effects as a window to generalization: Separating decisional and perceptual sequential effects in category learning.

Accounts of learning and generalization typically focus on factors related to lasting changes in representation (i.e., long-term memory). The authors present evidence that shorter term effects also play a critical role in determining performance and that these recency effects can be subdivided into perceptual and decisional components. Experimental results based on a probabilistic category structure show that the previous stimulus exerts a contrastive effect on the current percept (perceptual recency) and that responses are biased toward or away from the previous feedback, depending on the similarity between successive stimuli (decisional recency). A method for assessing these recency effects is presented that clarifies open questions regarding stimulus generalization and perceptual contrast effects in categorization and in other domains. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contrasting object-based and texture-based accounts of same/different discrimination learning with trial-unique stimuli.

Same/different discrimination is a classic task for investigating relational learning in animals. Recent research suggests that pigeons can learn a trial-unique same/different discrimination, which eliminates the opportunity to memorize the training items (Brooks & Wasserman, 2008). The authors conducted three tests to elucidate the role that item-based comparison plays in this trial-unique discrimination. In the first, the authors tested the possibility that pigeons’ same/different discrimination was based on textural features of the displays by creating a single, unitary texture from same and different displays; pigeons failed to discriminate these unitary textural displays. In the second, the authors varied the number of items (mosaics) in the display and the authors reproduced the characteristic decline in performance associated with fewer items. In the third, the authors systematically increased the area of two mosaics to closely match the area occupied by increasing numbers of mosaics; the results obtained with two small items persisted even when the size of the mosaics was increased. These results clearly show that pigeons’ same/different discrimination was based on object-level variability and not on other properties of the displays. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of punishment (electric shock) on perceptual learning.

3 experiments were conducted to explore the consequences of the association of punishment with percepts and to trace its residual effects. Electric shock was associated with tactual profiles of faces. Voltage, temporal contiguity, and ability to escape shock were varied. The results showed that there was more reporting of the non-shocked profile as intensity of shock increased, that escape conditions lead to more reporting of the shocked profiles, the shocked profile is recalled more vividly, and as the delay between exposure and recall increases there is more reporting of the nonshocked profile. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extending the simultaneous-sequential paradigm to measure perceptual capacity for features and words.

In perception, divided attention refers to conditions in which multiple stimuli are relevant to an observer. To measure the effect of divided attention in terms of perceptual capacity, we introduce an extension of the simultaneous-sequential paradigm. The extension makes predictions for fixed-capacity models as well as for unlimited-capacity models. We apply this paradigm to two example tasks, contrast discrimination and word categorization, and find dramatically different effects of divided attention. Contrast discrimination has unlimited capacity, consistent with independent, parallel processing. Word categorization has a nearly fixed capacity, consistent with either serial processing or fixed-capacity, parallel processing. We argue that these measures of perceptual capacity rely on relatively few assumptions compared to most alternative measures. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Subliminal processing of smoking-related and affective stimuli in tobacco addiction.

Cognitive processing biases toward smoking-related and affective cues may play a role in tobacco dependence. Because processing biases may occur outside conscious awareness, the current study examined processing of smoking-related and affective stimuli presented at subliminal conditions. A pictorial subliminal repetition priming task was administered to three groups: (1) Nonsmokers (n = 56); (2) Smokers (≥10 cigarettes/day) who had been deprived from smoking for 12 h (n = 47); and (3) Nondeprived smokers (n = 66). Prime stimuli were presented briefly (17 ms) and were followed by a mask (to render them unavailable to conscious awareness) and then a target. Participants were required to make a speeded classification to the target. A posttask awareness check was administered to ensure that participants could not consciously perceive the briefly presented primes (i.e., smoking paraphernalia, neutral office supplies, and happy, angry, and neutral facial expressions). The groups differed in the degree to which they exhibited a processing bias for smoking-related stimuli, F(2, 166) = 4.99, p = .008. Deprived smokers exhibited a bias toward processing smoking (vs. neutral office supply) stimuli, F(1, 46) = 5.67, p = .02, whereas nondeprived smokers and nonsmokers did not (ps > .22). The three groups did not differ in the degree to which they exhibited a subliminal processing bias for affective stimuli. Tobacco deprivation appears to increase smokers' subliminal processing of smoking-related (vs. neutral) stimuli but does not influence subliminal processing of affective stimuli. Future research should investigate whether subliminal biases toward smoking-related stimuli influence relapse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Separating perceptual and decisional attention processes in the identification and categorization of integral-dimension stimuli.

Four observers performed matching, identification, and categorization with stimuli that varied along the integral dimensions: brightness and saturation. General recognition theory (F. G. Ashby & J. T. Townsend, 1986) was applied to quantify the separate influences of perceptual and decisional processes within and across tasks, with a focus on separating perceptual from decisional attention processes. Good accounts of the identification data were obtained from perceptual matching representation. This perceptual representation provided a good account of the categorization data, except when decisional selective attention to 1 stimulus dimension was required. Decisional selective attention reduced the attended-dimension perceptual variance relative to the unattended-dimension perceptual variance, with a larger reduction resulting when brightness, as opposed to saturation was attended. Implications for color vision research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Boosting cholinergic activity in gustatory cortex enhances the salience of a familiar conditioned stimulus in taste aversion learning.

The cholinergic system is important for learning, memory, and responses to novel stimuli. Exposure to novel, but not familiar, tastes increases extracellular acetylcholine (ACh) levels in insular cortex (IC). To further examine whether cholinergic activation is a critical signal of taste novelty, in these studies carbachol, a direct cholinergic agonist, was infused into IC before conditioned taste aversion (CTA) training with a familiar taste. By mimicking the cholinergic activation generated by novel taste exposure, it was hypothesized that a familiar taste would be treated as novel and therefore a salient target for aversion learning. As predicted, rats infused with the agonist were able to acquire CTAs to familiar saccharin. Effects of carbachol infusion on patterns of neuronal activation during conditioned stimulus–unconditioned stimulus pairing were assessed using Fos-like immunoreactivity (FLI). Familiar taste–illness pairing following carbachol, but not vehicle, induced significant elevations of FLI in amygdala, a region with reciprocal connections to IC that is also important for CTA learning. These results support the view that IC ACh activity provides a critical signal of taste novelty that facilitates CTA acquisition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)