Effect of temporal and spatial stimulus relationships in controlled perceptual learning upon disappearances observed under reduced stimulation conditions

Perceptual learning was studied under reduced stimulation conditions. Simply as a result of previous close temporal and spatial concurrence, discriminably different stimuli disappear together more frequently than without such association. Simultaneous concurrence of the stimuli was more efficient than sequential in the development of associations. Other temporal and spatial stimulus-stimulus relationships were manipulated, and the results are discussed.     

Effect of amount of perceptual learning upon disappearances observed under reduced stimulation conditions

Perceptual learning was studied under reduced stimulation conditions. We found that, simply as a result of previous close temporal and spatial concurrence, discriminably different stimuli disappear together more frequently than without such association. Moreover, it was shown that the extent to which the stimuli subsequently “operated” together was a linear function of the-frequency of the previous joint occurrence.     

Visual perceptual learning

Perceptual learning refers to the phenomenon that practice or training in perceptual tasks often substantially improves perceptual performance. Often exhibiting stimulus or task specificities, perceptual learning differs from learning in the cognitive or motor domains. Research on perceptual learning reveals important plasticity in adult perceptual systems, and as well as the limitations in the information processing of the human observer. In this article, we review the behavioral results, mechanisms, physiological basis, computational models, and applications of visual perceptual learning.     

Late maturation of auditory perceptual learning

Adults can improve their performance on many perceptual tasks with training, but when does the response to training become mature? To investigate this question, we trained 11‐year‐olds, 14‐year‐olds and adults on a basic auditory task (temporal‐interval discrimination) using a multiple‐session training regimen known to be effective for adults. The adolescents all began with performance in the adult range. However, while all of the adults improved across sessions, none of the 11‐year‐olds and only half of the 14‐year‐olds did. The adolescents who failed to learn did so even though the 10‐session training regimen provided twice the number of sessions required by adults to reach asymptotic performance. Further, over the course of each session, the performance of the adults was stable but that of the adolescents, including those who learned, deteriorated. These results demonstrate that the processes that underlie perceptual learning can continue to develop well into adolescence.     

Visual training improves perceptual grouping based on basic stimulus features

Training on visual tasks improves performance on basic and higher order visual capacities. Such improvement has been linked to changes in connectivity among mediating neurons. We investigated whether training effects occur for perceptual grouping. It was hypothesized that repeated engagement of integration mechanisms would enhance grouping processes. Thirty-six participants underwent 15 sessions of training on a visual discrimination task that required perceptual grouping. Participants viewed 20?×?20 arrays of dots or Gabor patches and indicated whether the array appeared grouped as vertical or horizontal lines. Across trials stimuli became progressively disorganized, contingent upon successful discrimination. Four visual dimensions were examined, in which grouping was based on similarity in luminance, color, orientation, and motion. Psychophysical thresholds of grouping were assessed before and after training. Results indicate that performance in all four dimensions improved with training. Training on a control condition, which paralleled the discrimination task but without a grouping component, produced no improvement. In addition, training on only the luminance and orientation dimensions improved performance for those conditions as well as for grouping by color, on which training had not occurred. However, improvement from partial training did not generalize to motion. Results demonstrate that a training protocol emphasizing stimulus integration enhanced perceptual grouping. Results suggest that neural mechanisms mediating grouping by common luminance and/or orientation contribute to those mediating grouping by color but do not share resources for grouping by common motion. Results are consistent with theories of perceptual learning emphasizing plasticity in early visual processing regions.     

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.     

Effect of an auditory stimulus on the processing of a visual stimulus under single- and dual-tasks conditions

The Sternberg Additive Factor Method was used to draw inferences about the flow of information under single- and dual-tasks conditions which were identical in terms of the stimuli involved but different in terms of response requirements. In both conditions, subjects pressed a left- or right-hand key in response to the onset of an X or O (intact or degraded) which was accompanied by a monaural or binaural tone. In the dual-tasks condition, subjects responded verbally to the tone location while also making the key-press response, whereas, in the single-task condition, no response to the tone was required. The pattern of main effects and interactions suggested that the same model of information flow described both single- and dual-tasks conditions; i.e., visual and auditory stimuli were encoded separately but shared capacity at the response selection stage.     

Visual perceptual learning by operant conditioning training follows rules of contingency

Visual perceptual learning (VPL) can occur as a result of a repetitive stimulus-reward pairing in the absence of any task. This suggests that rules that guide Conditioning, such as stimulus-reward contingency (e.g., that stimulus predicts the likelihood of reward), may also guide the formation of VPL. To address this question, we trained subjects with an operant conditioning task in which there were contingencies between the response to one of three orientations and the presence of reward. Results showed that VPL only occurred for positive contingencies, but not for neutral or negative contingencies. These results suggest that the formation of VPL is influenced by similar rules that guide the process of Conditioning.     

Visual and auditory accessory stimulus offset and the Simon effect

We investigated the effect on the right and left responses of the disappearance of a task-irrelevant stimulus located on the right or left side. Participants pressed a right or left response key on the basis of the color of a centrally located visual target. Visual (Experiment 1) or auditory (Experiment 2) task-irrelevant accessory stimuli appeared or disappeared at locations to the right or left of the central target. In Experiment 1, responses were faster when onset or offset of the visual accessory stimulus was spatially congruent with the response. In Experiment 2, responses were again faster when onset of the auditory accessory stimulus and the response were on the same side. However, responses were slightly slower when offset of the auditory accessory stimulus and the response were on the same side than when they were on opposite sides. These findings indicate that transient change information is crucial for a visual Simon effect, whereas sustained stimulation from an ongoing stimulus also contributes to an auditory Simon effect.     

Confidence and decision type under matched stimulus conditions: overconfidence in perceptual but not conceptual decisions

Within the domain of metacognition, there is disagreement whether different processes underlie evaluations of confidence in perceptual versus conceptual decisions. The relationship between confidence and accuracy for perceptual and conceptual decisions was compared using newly created stimuli that could be used to elicit either decision type. Based on theories of Brunswikian and Thurstonian uncertainties, significant underconfidence for perceptual decisions and overconfidence for conceptual decisions were predicted. Three within‐subjects experiments did not support this hypothesis. Participants showed significant overconfidence for perceptual decisions and no overconfidence for conceptual decisions. In addition, significant hard‐easy effects were consistently found for both decision types. Incorporating our findings with past results reveals that both over‐ and underconfidence are attainable on perceptual tasks. This conclusion, in addition to the common presence of hard‐easy effects and significant across‐task correlations in over/underconfidence, suggests that confidence judgments for the two decision types may depend on largely shared processes. Possible contributions to confidence and over/underconfidence are explored, focusing on response time factors and participants' knowledge bases. Copyright © 2007 John Wiley & Sons, Ltd.     

Temporal specificity of perceptual learning in an auditory discrimination task

Although temporal processing is used in a wide range of sensory and motor tasks, there is little evidence as to whether a single centralized clock or a distributed system underlies timing in the range of tens to hundreds of milliseconds. We investigated this question by studying whether learning on an auditory interval discrimination task generalizes across stimulus types, intervals, and frequencies. The degree to which improvements in timing carry over to different stimulus features constrains the neural mechanisms underlying timing. Human subjects trained on a 100- or 200-msec interval discrimination task showed an improvement in temporal resolution. This learning generalized to a perceptually distinct duration stimulus, as well as to the trained interval presented with tones at untrained spectral frequencies. The improvement in performance did not generalize to untrained intervals. To determine if spectral generalization was dependent on the importance of frequency information in the task, subjects were simultaneously trained on two different intervals identified by frequency. As a whole, our results indicate that the brain uses circuits that are dedicated to specific time spans, and that each circuit processes stimuli across nontemporal stimulus features. The patterns of generalization additionally indicate that temporal learning does not rely on changes in early, subcortical processing, because the nontemporal features are encoded by different channels at early stages.     

The time course of neural changes underlying auditory perceptual learning

Improvement in perception takes place within the training session and from one session to the next. The present study aims at determining the time course of perceptual learning as revealed by changes in auditory event-related potentials (ERPs) reflecting preattentive processes. Subjects were trained to discriminate two complex auditory patterns in a single session. ERPs were recorded just before and after training, while subjects read a book and ignored stimulation. ERPs showed a negative wave called mismatch negativity (MMN)—which indexes automatic detection of a change in a homogeneous auditory sequence—just after subjects learned to consciously discriminate the two patterns. ERPs were recorded again 12, 24, 36, and 48 h later, just before testing performance on the discrimination task. Additional behavioral and neurophysiological changes were found several hours after the training session: an enhanced P2 at 24 h followed by shorter reaction times, and an enhanced MMN at 36 h. These results indicate that gains in performance on the discrimination of two complex auditory patterns are accompanied by different learning-dependent neurophysiological events evolving within different time frames, supporting the hypothesis that fast and slow neural changes underlie the acquisition of improved perception.     

Analysis of the perceptual learning effect in flavour aversion learning: Evidence for stimulus differentiation

Rats received exposure to two compound flavours, AX and BX, where A and B were sucrose and saline and X was acid. For group intermixed (I), exposure consisted of alternating trials with AX and BX; group blocked (B) received a block of AX trials and a separate block of BX trials. Experiment 1 showed that generalization to BX after conditioning with AX was less profound in group I than in group B. Separate examination of the elements of the compound showed that the source of this difference lay in the strength acquired by the X element. X acquired less strength in group I than in group B (Experiments 1 and 2), whereas for the A element (Experiments 3 and 4) the reverse pattern was obtained. These results support the proposal that the perceptual learning effect (restricted generalization from AX to BX in group I) depends on a process that enhances the effectiveness of unique stimulus elements (A and B) and reduces that of common elements (such as X).     

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.     

The perceptual integration of auditory stimulus edges: an illusory short tone in stimulus patterns consisting of two partly overlapping glides

Two partly overlapping frequency glides can be perceived as consisting of a long pitch trajectory accompanied by a short tone in the temporal middle. It was found that the appearance of this middle tone could not be related to peripheral processes concerned with spectral splatter or combination tones that could have emerged during the overlap of the glides. Furthermore, it was found that the middle tone was perceived even when components of the 2 glides were separated by more than an equivalent rectangular bandwidth at any time during the overlap. The appearance of the middle tone indicates that auditory events can result from the perceptual integration of component parts-that is, stimulus edges-of acoustically different sounds.