The role of stimulus comparison in human perceptual learning: Effects of distractor placement.

Within-subjects procedures were used to assess the influence of stimulus comparison on perceptual learning in humans. In Experiment 1, participants received intermixed (A, A′, A, A′,…) or blocked (B, B,…, B′, B′,…) exposure to pairs of similar female faces. In a subsequent same/different discrimination task, participants were more accurate when the test involved A and A′ than when it involved B and B′ (or novel faces: C and C′). This perceptual learning effect was reduced by placing a visual distractor (*: either another face or a checkerboard) between successive presentations of the faces during the exposure stage (e.g., A – * – A′). The attenuation of the intermixed versus blocked difference was particularly marked when faces were used as the distractor. In Experiment 2, this reduction in perceptual learning was more marked when * was positioned between the pairs of intermixed faces (i.e., A – * – A′) than when it preceded and succeeded those faces (i.e., * – A – A′ – *). These results provide the first direct evidence that the opportunity to compare stimuli plays a causal role in supporting perceptual learning. They also support the specific view that perceptual learning reflects an interaction between a short-term habituation process, that ordinarily biases processing away from the frequently presented common elements and toward their less frequently presented unique elements, and a long-term representational process that reflects this bias. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The role of stimulus comparison in perceptual learning: an investigation with the domestic chick

In two experiments an imprinting procedure was used to familiarize chicks with two stimuli, A and B, that subsequently served as the discriminanda in a simultaneous discrimination. On the first day of each experiment, subjects either received presentations of A and B that were intermixed within a session (mixed exposure) or presentations of A in one session and of B in another (separate exposure). For half of the subjects in each of the exposure conditions, A and B differed in both colour and form; for the remainder A and B differed in form alone. On the second day of the experiments, the chicks were placed into a cool test apparatus and given training in which approaching A was rewarded by the delivery of a stream of warm air, but approaching B was not. Acquisition of this discrimination was more rapid when A and B differed in two respects than when they differed in form alone. When A and B differed in both colour and form, the heat-reinforced discrimination was acquired more rapidly after separate exposure than after mixed exposure; but when A and B differed in form alone, discrimination learning was more rapid following mixed exposure than separate exposure. The latter finding, that the opportunity to compare stimuli differing in only one dimension facilitates subsequent discrimination learning, is consistent with earlier suggestions (Gibson, 1969) regarding the conditions that promote perceptual learning.     

Memory for, and salience of, the unique features of similar stimuli in perceptual learning.

In two experiments, participants received exposure to complex checkerboards (e.g., AX and BX) that consisted of small distinctive features (A and B) superimposed on a larger common background (X). Subsequent discrimination between AX and BX, assessed by a same-different task, was facilitated when the stimuli were presented on alternate trials in preexposure—a perceptual learning effect (Experiment 1). The hypothesis that this form of exposure results in more accurate representations of the unique features was supported in Experiment 1, which showed that participants were well able to match the color of the feature with its shape. Experiment 2 showed that exposure to A and B in isolation, intermixed with presentations of AX and BX, enhanced the perceptual learning effect, which confirmed that the better encoding of the unique features during intermixed preexposure is a direct cause of the enhanced discrimination observed following preexposure on this schedule. (PsycINFO Database Record (c) 2011 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)     

Some factors that determine the influence of a stimulus that is irrelevant to a discrimination.

In 5 autoshaping experiments pigeons received 3 stimuli, A, B, and C, for a discrimination in which food was presented after the simultaneous compounds AC and BC, but not after the simultaneous compound ABC. The ease with which this discrimination was mastered was facilitated by presenting C continuously throughout each session (Experiment 1), by presenting C by itself for nonreinforced trials (Experiment 2), and by pairing C by itself consistently with food (Experiment 3). Presenting C by itself and pairing it with food according to a partial reinforcement schedule had no significant influence on the acquisition of the discrimination (Experiments 4 and 5). The results are consistent with a configural theory of associative learning that suggests that experience with a stimulus alters its salience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallel and competitive processes in hierarchical analysis: Perceptual grouping and encoding of closure.

The role of perceptual grouping and the encoding of closure of local elements in the processing of hierarchical patterns was studied. Experiments 1 and 2 showed a global advantage over the local level for 2 tasks involving the discrimination of orientation and closure, but there was a local advantage for the closure discrimination task relative to the orientation discrimination task. Experiment 3 showed a local precedence effect for the closure discrimination task when local element grouping was weakened by embedding the stimuli from Experiment 1 in a background made up of cross patterns. Experiments 4A and 4B found that dissimilarity of closure between the local elements of hierarchical stimuli and the background figures could facilitate the grouping of closed local elements and enhanced the perception of global structure. Experiment 5 showed that the advantage for detecting the closure of local elements in hierarchical analysis also held under divided- and selective-attention conditions. Results are consistent with the idea that grouping between local elements takes place in parallel and competes with the computation of closure of local elements in determining the selection between global and local levels of hierarchical patterns for response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A spatial frequency account of the detriment that local processing of Navon letters has on face recognition.

Five minutes of processing the local features of a Navon letter causes a detriment in subsequent face-recognition performance (Macrae & Lewis, 2002). We hypothesize a perceptual after effect explanation of this effect in which face recognition is less accurate after adapting to high-spatial frequencies at high contrasts. Five experiments were conducted in which face-recognition performance was compared after processing high-contrast Navon stimuli. The standard recognition deficit was observed for processing the local features of Navon stimuli, but not if the stimuli were blurred (Experiment 1) or if they were of lower contrast (Experiment 2). A face-recognition deficit was observed after processing small, high-contrast letters equivalent to local processing of Navon letters (Experiment 3). Experiments 4 and 5 demonstrated that recognition of bandpass-filtered faces interacted with the type of Navon processing, in which the recognition of low-pass filtered faces was better following local rather than global processing. These results suggest that the Navon effect on subsequent face recognition is a perceptual phenomenon. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Applying the attractor field model to social cognition: Perceptual discrimination is facilitated, but memory is impaired for faces displaying evaluatively congruent expressions.

A new model of mental representation is applied to social cognition: the attractor field model. Using the model, the authors predicted and found a perceptual advantage but a memory disadvantage for faces displaying evaluatively congruent expressions. In Experiment 1, participants completed a same/different perceptual discrimination task involving morphed pairs of angry-to-happy Black and White faces. Pairs of faces displaying evaluatively incongruent expressions (i.e., happy Black, angry White) were more likely to be labeled as similar and were less likely to be accurately discriminated from one another than faces displaying evaluatively congruent expressions (i.e., angry Black, happy White). Experiment 2 replicated this finding and showed that objective discriminability of stimuli moderated the impact of attractor field effects on perceptual discrimination accuracy. In Experiment 3, participants completed a recognition task for angry and happy Black and White faces. Consistent with the attractor field model, memory accuracy was better for faces displaying evaluatively incongruent expressions. Theoretical and practical implications of these findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential and simultaneous feature positive discriminations: Occasion setting and configural learning in human Pavlovian conditioning.

Using a conditioned suppression preparation, the authors investigated sequential (X→A+/A–) versus simultaneous (XA+/A–) feature positive (FP) discrimination learning in humans. The sequential discrimination was expected to be resolved by means of a Feature X Modulated Target A–US association and the simultaneous discrimination by a feature X–US association. After sequential FP training, extinction of Feature X did not affect discriminative X→A/A responding (Experiment 1), and X transferred its modulatory ability only to new targets, B, that had also been modulated (Experiment 2). This suggests that the sequential FP discrimination indeed resulted in occasion setting. Unlike expected, Feature X Extinction did not affect discriminative XA/A responding after simultaneous FP training (Experiment 3), while at the same time Feature X did show the predicted nonselective transfer to new targets, B (Experiment 4). J. M. Pearce's (1987) configural learning theory can account for most but not all findings of Experiments 3 and 4. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Configural processes in human associative learning.

The extent to which human discrimination learning is based on elemental or configural stimulus representations was examined in 7 experiments. In Experiments 1a and 1b, participants were able to learn nonlinear discrimination problems in a food-allergy task. In unique-cue theories, such learning is explained by individual stimulus elements acquiring independent connections with the outcome and also combining to form unique cues that function elementally. In Stage 1 of Experiments 2, 3, and 4a–c, Food A signaled an allergy outcome (O) (A?→?O) when presented alone but signaled no allergy (AB?→?no O) when paired with Food B. In Stage 2, Food B was paired with the allergy (B?→?0). In a test phase, the original discrimination between A and AB was found to be intact, at variance with the unique-cue theory. By contrast, in Experiments 5a, 5b, and 6, an effect of the B?→?O trials on the A–AB discrimination was observed with training procedures previously found by D. A. Williams (1995) to encourage elemental processing. Experiment 7 showed that the influence of B?→?0 trials on the A–AB discrimination was unaffected by pretreatments designed to foster an elemental processing strategy.… (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contextual control in discrimination reversal learning.

In 3 human predictive learning experiments, the authors examined contextual control of responding in discrimination reversal learning. In Phase 1, a discrimination between 2 stimuli (A+, B-) was trained in Context 1. During Phase 2, participants received discrimination reversal training (A-, B+) in Context 2. Testing occurred in Context 1 and Context 2 (Experiments 1A and 1B) or in Context 1 and Context 3 (Experiment 2). During the test phase, performance in Context 1 and Context 2 reflected the contingencies trained during Phase 1 and Phase 2, respectively. When testing occurred in Context 3, there was no discriminative responding between A and B. In addition, the experiments demonstrated that discriminating stimuli with a consistent reinforcement history were also affected by contextual manipulations. Results indicate that each training context acquires the ability to control performance. Unique-cue and configural approaches account for a major part of the results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The mere exposure effect in patients with Alzheimer's disease.

The mere exposure effect was examined in patients with mild to moderate Alzheimer's disease (AD). Twenty patients and 20 elderly controls judged the physical characteristics of faces. Implicit memory was tested later by presenting pairs of faces (old and new) and asking participants which faces they liked better. Patients and controls exhibited above chance preference for previously exposed faces. Experiment 2 evaluated whether the preserved implicit memory of patients was mediated by explicit memory. Patients and controls again judged faces but then later chose which faces they had seen before. Patients exhibited impaired recognition memory compared to controls. These findings suggest that a mere exposure affect for unfamiliar faces is present in mild to moderate AD. The results are discussed in terms of perceptual and conceptual priming and relatively spared occipital lobe functioning in early AD. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Does perceived race affect discrimination and recognition of ambiguous-race faces? A test of the sociocognitive hypothesis.

Discrimination and recognition are often poorer for other-race than own-race faces. These other-race effects (OREs) have traditionally been attributed to reduced perceptual expertise, resulting from more limited experience, with other-race faces. However, recent findings suggest that sociocognitive factors, such as reduced motivation to individuate other-race faces, may also contribute. If the sociocognitive hypothesis is correct, then it should be possible to alter discrimination and memory performance for identical faces by altering their perceived race. We made identical ambiguous-race morphed faces look either Asian or Caucasian by presenting them in Caucasian or Asian face contexts, respectively. However, this perceived-race manipulation had no effect on either discrimination (Experiment 1) or memory (Experiment 2) for the ambiguous-race faces, despite the presence of the usual OREs in discrimination and recognition of unambiguous Asian and Caucasian faces in our participant population. These results provide no support for the sociocognitive hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of superexcitatory properties by an irrelevant background stimulus.

Six appetitive conditioning experiments with rats demonstrated that an irrelevant X accompanying a negative patterning discrimination (XA+, XB+, XAB-) acquires extraordinarily high levels of conditioned excitation. Responding to X was similar to that evoked by 2 excitors in combination (Experiment 1) and was greater than responding to a separately reinforced Y (Experiments 2-5). Superexcitatory properties were not acquired by X in the nonpatterning discriminations of Experiments 2-4. Experiment 5 found that A and B, if anything, were weakly excitatory. Making them more strongly excitatory after conditioning did not interfere with retention of the original discrimination (Experiment 6). Results support a counterintuitive prediction of associative theories that, under carefully arranged conditions, irrelevant stimuli may acquire superexcitatory properties. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Race as a visual feature: Using visual search and perceptual discrimination tasks to understand face categories and the cross-race recognition deficit.

One of the most familiar empirical phenomena associated with face recognition is the cross-race (CR) recognition deficit whereby people have difficulty recognizing members of a race different from their own. Most researchers assume that the CR deficit is caused by failure to generalize perceptual encoding expertise from same-race (SR) faces to CR faces. However, this explanation ignores critical differences in the social cognitions and feature coding priorities associated with SR and CR faces. On the basis of data from visual search and perceptual discrimination tasks, it appears that the deficit occurs because people emphasize visual information specifying race at the expense of individuating information when recognizing CR faces. In particular, it is possible to observe a paradoxical improvement in both detection and perceptual discrimination accuracy for CR faces that is limited to those who recognize them poorly. These findings support a new explanation for the CR recognition deficit based on feature coding differences between CR and SR faces, and appear incompatible with similarity-based models of face categories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The Facilitated Processing of Threatening Faces: An ERP Analysis.

Threatening, friendly, and neutral faces were presented to test the hypothesis of the facilitated perceptual processing of threatening faces. Dense sensor event-related brain potentials were measured while subjects viewed facial stimuli. Subjects had no explicit task for emotional categorization of the faces. Assessing early perceptual stimulus processing, threatening faces elicited an early posterior negativity compared with nonthreatening neutral or friendly expressions. Moreover, at later stages of stimulus processing, facial threat also elicited augmented late positive potentials relative to the other facial expressions, indicating the more elaborate perceptual analysis of these stimuli. Taken together, these data demonstrate the facilitated perceptual processing of threatening faces. Results are discussed within the context of an evolved module of fear (A. Ohman & S. Mineka, 2001). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dominance of global visual properties at birth.

Six experiments are reported that were aimed at demonstrating the presence in newborns of a perceptual dominance of global over local visual information in hierarchical patterns, similar to that observed in adults (D. Navon, 1977, 1981). The first four experiments showed that, even though both levels of visual information were detectable by the newborn (Experiments 1A and 1B), global cues enjoyed some advantage over local cues (Experiments 2 and 3). Experiments 4A and 4B demonstrated that the global bias was strictly dependent on the low spatial frequency content of the stimuli and vanished after selective removal of low spatial frequencies. The results are interpreted as suggesting parallels between newborns' visual processing and processing later in development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The affiliation motive and perceptual sensitivity to faces.

An attempt was made to predict from imaginative measures of the affiliation motive the frequency with which S selects human faces from similar but nonhuman figures in a perceptual task. The Ss were 93 male undergraduates who responded to pictures with imaginative stories scored for n Affiliation. A month later they were introduced to the perceptual task which required that they state which of 4 figures flashed on a screen was clearest, all stimuli being below the recognition threshold. On each trial 1 of the 4 stimuli was a face and the others were similar but affiliation-neutral. Ss high in n Affiliation recognized faces significantly more frequently than those low in n Affiliation. Thus, the predicted relationship between motivation and the perceptual selection of motive-relevant stimuli was supported. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Deficits in other-race face recognition: No evidence for encoding-based effects.

The other-race effect (ORE) in face recognition is typically observed in tasks which require long-term memory. Several studies, however, have found the effect early in face encoding (Lindsay, Jack, & Christian, 1991; Walker & Hewstone, 2006). In 6 experiments, with over 300 participants, we found no evidence that the recognition deficit associated with the ORE reflects deficits in immediate encoding. In Experiment 1, with a study-to-test retention interval of 4 min, participants were better able to recognise White faces, relative to Asian faces. Experiment 1 also validated the use of computer-generated faces in subsequent experiments. In Experiments 2 through 4, performance was virtually identical to Asian and White faces in match-to-sample, immediate recognition. In Experiment 5, decreasing target-foil similarity and disrupting the retention interval with trivia questions elicited a re-emergence of the ORE. Experiments 6A and 6B replicated this effect, and showed that memory for Asian faces was particularly susceptible to distraction; White faces were recognised equally well, regardless of trivia questions during the retention interval. The recognition deficit in the ORE apparently emerges from retention or retrieval deficits, not differences in immediate perceptual processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Negative priming in associative learning: Evidence from a serial-habituation procedure.

Rats received exposure to two serial compounds (A-X and B-Y) comprising auditory stimuli (A and B) followed by localized visual stimuli (X and Y). A and B came to elicit responses that reflected the location of X and Y (Experiment 1). The orienting response (OR) elicited by X and Y declined during exposure to the A-X and B-Y compounds and was restored on trials when A preceded Y, and B preceded X (Experiments 2 and 3). These results, observed with use of relatively neutral stimuli, parallel those observed during Pavlovian conditioning and provide support for A. R. Wagner's ( 1981) account of associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)