Perceptual Learning Effects Research Articles

Perceptual learning effect underlying material categorization tasks

Perceptual learning effect underlying material categorization tasks

Effects of face view discrimination learning on N170 latency and amplitude

Learning is critical for fast and efficient object recognition. However, the neural implementation of object learning in the human brain remains largely unknown. Using combined psychophysics and electroencephalogram (EEG), we investigated the effects of perceptual learning on face processing. Human subjects were trained to discriminate face views at an in-depth face orientation (i.e. 30°) over eight daily sessions, which resulted in a significant improvement in sensitivity to the trained face view. Psychophysical results showed that this improvement was highly specific to the trained view. Before and after training, we recorded subjects’ EEG signals responding to the trained and the untrained face views. Analyses of event-related potentials (ERPs) showed that face view discrimination training led to a larger reduction of N170 latency at the left occipital–temporal area with the trained face view, compared with the untrained ones. These findings provide evidence for the facilitation model on neuronal plasticity from visual experience, suggesting a faster processing speed of face induced by perceptual learning.

Changes in prefrontal neuronal activity after learning to perform a spatial working memory task.

The prefrontal cortex is considered essential for learning to perform cognitive tasks though little is known about how the representation of stimulus properties is altered by learning. To address this issue, we recorded neuronal activity in monkeys before and after training on a task that required visual working memory. After the subjects learned to perform the task, we observed activation of more prefrontal neurons and increased activity during working memory maintenance. The working memory-related increase in firing rate was due mostly to regular-spiking putative pyramidal neurons. Unexpectedly, the selectivity of neurons for stimulus properties and the ability of neurons to discriminate between stimuli decreased as the information about stimulus properties was apparently present in neural firing prior to training and neuronal selectivity degraded after training in the task. The effect was robust and could not be accounted for by differences in sampling sites, selection of neurons, level of performance, or merely the elapse of time. The results indicate that, in contrast to the effects of perceptual learning, mastery of a cognitive task degrades the apparent stimulus selectivity as neurons represent more abstract information related to the task. This effect is countered by the recruitment of more neurons after training.

Effect of extended training on generalization of latent inhibition: An instance of perceptual learning

Four experiments examined generalization of latent inhibition (LI) as a function of the length of preexposure in a conditioned taste aversion procedure with rats. Experiment 1 showed that one or four nonreinforced presentations of a flavor compound (BX) retarded subsequent conditioning to another compound (AX). However, after eight presentations of BX, conditioning to AX occurred at the same rate as with no preexposure. These results indicate that generalization of LI decreased as the length of preexposure to BX increased. Experiment 2 replicated this effect of reducing generalization, as well as demonstrating that LI actually increased as the length of preexposure to AX increased. Experiment 3 extended the generality of the effect to a procedure in which both BX and AX were preexposed. Experiment 4 demonstrated a similar reducing-generalization effect when generalization of LI from BX to X was assessed. All of these data are consistent with the notion that prolonged preexposure to BX enhances its discriminability. Different learning mechanisms that might be responsible for this perceptual learning effect are discussed.

Specialization for written words over objects in the visual cortex

The Visual Word Form Area (VWFA) is part of the left ventral visual stream that underlies the invariant identification of visual words. It remains debated whether this region is truly selective for words relative to common objects; why this particular part of the visual system is reproducibly engaged in reading; and whether reading expertise also relies on perceptual learning within earlier visual areas. In this fMRI study we matched written words and line-drawings of objects in luminance, contour length and number of features. We then compared them to control images made by scrambling procedures that kept local features intact. Greater responses to written words than to objects were found not only in the VWFA, but also in areas V1/V2 and V3v/V4. Furthermore, by contrasting stimuli reduced either to line junctions (vertices) or to line midsegments, we showed that the VWFA partially overlaps with regions of ventral visual cortex particularly sensitive to the presence of line junctions that are useful for object recognition. Our results indicate that preferential processing of written words can be observed at multiple levels of the visual system. It is possible that responses in early visual areas might be due to some remaining differences between words and controls not eliminated in the present stimuli. However, our results concur with recent comparisons of literates and illiterates and suggest that these early visual activations reflect the effects of perceptual learning under pressure for fast, parallel processing that is more prominent in reading than other visual cognitive processes.

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.

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.

Perceptual learning, aging, and improved visual performance in early stages of visual processing

In the present study, we examined whether perceptual learning methods can be used to improve performance of older individuals. Subjects performed a texture discrimination task in the peripheral visual field and a letter discrimination task in central vision. The SOA threshold was derived by presenting a mask following the stimuli. Older subjects (age greater than 65 years) were either trained for 2 days using near threshold stimuli (experimental group) or were trained with the task with supra-threshold stimuli (older control group). The experimental group showed significant improvement in the task as a result of training whereas the older control group showed no significant improvement. The improved performance post-training equaled that of a younger control group and was maintained for at least 3 months. The results of two additional experiments indicate that the improved performance was not due to changes in divided attention, that the effect of perceptual learning was location specific, and that the pattern of learning was similar to that of younger subjects. These results indicate that perceptual learning with near threshold training can be used to improve visual performance among older individuals, that the improvements are not the result of practice with the visual task, and that the improvements do not transfer to non-trained locations.

Cholinergic Enhancement Augments Magnitude and Specificity of Visual Perceptual Learning in Healthy Humans

Learning through experience underlies the ability to adapt to novel tasks and unfamiliar environments. However, learning must be regulated so that relevant aspects of the environment are selectively encoded. Acetylcholine (ACh) has been suggested to regulate learning by enhancing the responses of sensory cortical neurons to behaviorally relevant stimuli. In this study, we increased synaptic levels of ACh in the brains of healthy human subjects with the cholinesterase inhibitor donepezil (trade name: Aricept) and measured the effects of this cholinergic enhancement on visual perceptual learning. Each subject completed two 5 day courses of training on a motion direction discrimination task, once while ingesting 5 mg of donepezil before every training session and once while placebo was administered. We found that cholinergic enhancement augmented perceptual learning for stimuli having the same direction of motion and visual field location used during training. In addition, perceptual learning with donepezil was more selective to the trained direction of motion and visual field location. These results, combined with previous studies demonstrating an increase in neuronal selectivity following cholinergic enhancement, suggest a possible mechanism by which ACh augments neural plasticity by directing activity to populations of neurons that encode behaviorally relevant stimulus features.

Spatial frequency discrimination learning in normal and developmentally impaired human vision

Perceptual learning effects demonstrate that the adult visual system retains neural plasticity. If perceptual learning holds any value as a treatment tool for amblyopia, trained improvements in performance must generalise. Here we investigate whether spatial frequency discrimination learning generalises within task to other spatial frequencies, and across task to contrast sensitivity. Before and after training, we measured contrast sensitivity and spatial frequency discrimination (at a range of reference frequencies 1, 2, 4, 8, 16c/deg). During training, normal and amblyopic observers were divided into three groups. Each group trained on a spatial frequency discrimination task at one reference frequency (2, 4, or 8c/deg). Normal and amblyopic observers who trained at lower frequencies showed a greater rate of within task learning (at their reference frequency) compared to those trained at higher frequencies. Compared to normals, amblyopic observers showed greater within task learning, at the trained reference frequency. Normal and amblyopic observers showed asymmetrical transfer of learning from high to low spatial frequencies. Both normal and amblyopic subjects showed transfer to contrast sensitivity. The direction of transfer for contrast sensitivity measurements was from the trained spatial frequency to higher frequencies, with the bandwidth and magnitude of transfer greater in the amblyopic observers compared to normals. The findings provide further support for the therapeutic efficacy of this approach and establish general principles that may help develop more effective protocols for the treatment of developmental visual deficits.

Task transfer effects of contrast training and perceptual learning

Task transfer effects of contrast training and perceptual learning

Transfer of object learning across distinct visual learning paradigms

Perception and identification of visual stimuli improve with experience. This applies to both simple stimuli and complex objects, as shown in perceptual learning paradigms in which visual perception is challenged by degrading the stimuli, e.g. by backward masking or adding simultaneous noise. In each of these paradigms, perceptual learning is specific for the stimuli used during training. However, there can also be differences between paradigms, because they challenge the visual processing system in different ways. It is thus possible that paradigm-specific processes are needed to optimize performance. This would result in a failure of perceptual learning effects to generalize across paradigms. Here we present the first study designed to investigate whether visual object learning is specific to the type of stimulus degradation used during training. Sixteen participants were trained to recognize and name pictures of common objects. The stimulus set included 40 object images, but each participant was trained on only half of them. Half of the participants was trained in a backward masking paradigm, and the other half in a simultaneous noise addition paradigm. After five days, performance thresholds were measured in four tests: (1) the trained paradigm with the 20 trained objects, (2) the trained paradigm with the 20 new, untrained objects, (3) the untrained paradigm with the trained objects and (4) the untrained paradigm with new objects. Both groups showed a learning effect that increased gradually across days. These training effects were specific for the trained objects. In addition, an object-specific transfer to the untrained paradigm was found. The group trained in the simultaneous noise addition paradigm showed a complete transfer of performance to the backward masking task. The transfer was only partial when reversed. These findings indicate that both general learning processes and processes specific for the type of stimulus degradation are involved in perceptual learning.

Effects of perceptual learning on the temporal dynamics of perceptual decision

Effects of perceptual learning on the temporal dynamics of perceptual decision

Illusory shape pop out: Effects of perceptual learning

Illusory shape pop out: Effects of perceptual learning

Dynamic classification images reveal the effects of perceptual learning in a hyperacuity task

Dynamic classification images reveal the effects of perceptual learning in a hyperacuity task

Hemispheric specificity of perceptual learning effects under hard conditions

Hemispheric specificity of perceptual learning effects under hard conditions

Perceptual learning in human primary visual cortex

Repeated practice of perceptual tasks often produces marked improvements in behavioral performance. While such perceptual learning is found across a variety of visual tasks, physiological evidence of corresponding neural changes in humans has remained elusive. We hypothesized that practice of a task thought to be mediated by early visual mechanisms (i.e., simple contrast-detection) would produce measurable changes in human primary visual cortex (V1). Here were used fMRI to measure the effects of perceptual learning on activity in V1. Subjects spent more than twenty days (>10,000 trials) practicing detection of sinusoidal gratings. In order to quantify the specificity of learning, fMRI measurements and behavioral thresholds for contrast-detection and orientation-discrimination were collected before and after training for several eccentricities and grating orientations. We found that V1 responses for practiced gratings were reliably greater than those responses collected prior to training. Critically, the specificity of changes in V1 responses mirrored the specificity of changes in perceptual thresholds; both the changes in detection thresholds and V1 responses were orientation, and spatial-location specific. While these results are consistent with several models of the neural mechanisms of perceptual learning, the simplest explanation of our data may be a bottom-up gain change produced by a re-weighting of synaptic connections.

Perceptual learning in an appetitive Pavlovian procedure: Analysis of the effectiveness of the common element

Non-reinforced preexposure to two stimuli often enhances discrimination between them. Analyses of this perceptual learning phenomenon have mainly focused on the role played by the distinctive stimulus features; this study examined the contribution of the non-distinctive common elements. A standard appetitive Pavlovian procedure was used. Rats received two different schedules of exposure--alternated or blocked--to two compound auditory stimuli, AX and BX. In Experiment 1 a generalization test to BX that followed conditioning to AX showed that animals responded less, and hence discriminated better, following alternated exposure, thus extending the generality of this perceptual learning effect to standard appetitive Pavlovian procedures. The degree to which the common element X was mediating this effect was explored in the next three experiments. Experiment 2 assessed the effectiveness of X following conditioning to AX. Experiment 3 explored X's effectiveness throughout extensive conditioning to X. Experiment 4 tested the ability of X to overshadow a novel stimulus Y. The results were consistent with the suggestion that alternated preexposure can reduce the relative effectiveness of the common element.

How mechanical context and feedback jointly determine the use of mechanical variables in length perception by dynamic touch

Earlier studies have revealed that both mechanical context and feedback determine what mechanical invariant is used to perceive length by dynamic touch. In the present article, the authors examined how these two factors jointly constrain the informational variable that is relied upon. Participants were to judge length while wielding a rod or while holding it stationary. In two experiments, it was tested whether perceptual learning effects in the wielding condition transferred to the holding condition and vice versa. There was an asymmetry in transfer across mechanical conditions: Improvements in the holding context transferred to the wielding condition, but not vice versa. Examining the individuals' exploitation of mechanical variables, we found that, after feedback, participants changed in information usage in both mechanical conditions. For many participants, these changes were not confined to the mechanical context in which the feedback was provided. Indeed, feedback in one mechanical context brought about changes in information usage that often manifested themselves in the other mechanical condition. The authors explore the implications of these findings for research on perceptual learning in dynamic touch and the salience hypothesis.

Perceptual and neural pliability of odor objects.

A key function of the sense of smell is to guide organisms towards rewards and away from dangers. However, because relatively few volatile chemicals in the environment carry intrinsic biological value, the meaning of an odor often needs to be acquired through learning and experience. The tremendous perceptual and neural plasticity of the olfactory system provides a design that is ideal for the establishment of links between odor cues and behaviorally relevant events, promoting appropriate adaptive responses to foods, friends, foes, and mates. This article describes recent human neuroimaging data showing the dynamic effects of olfactory perceptual learning and aversive conditioning on the behavioral discrimination of odor objects, with parallel plasticity and reorganization in the posterior piriform and orbitofrontal cortices. The findings presented here highlight the important role of experience in shaping odor object perception and in ensuring the human sense of smell achieves its full perceptual potential.