Learning by Exposure in the Visual System (original) (raw)
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Attention alters visual plasticity during exposure-based learning
Current Biology, 2009
It is generally believed that attention enhances the processing of sensory information during perception and learning. Here we report that, contrary to common belief, attention limits the degree of plasticity induced by repeated exposure to image features. Specifically, daily exposure to oriented stimuli that are not linked to a specific task causes an orientation-specific improvement in perceptual performance along the "exposed" axes. This effect is modulated by attention: human subjects showed a larger improvement in orientation discrimination when attention is directed toward the location where stimuli are presented. However, the capacity to perform discriminations away from the exposed orientation is enhanced when the exposure stimuli are unattended. Importantly, the improvement in orientation discrimination at the unattended location leads to a robust enhancement in the discrimination of complex stimuli, such as natural texture images, with orientation components along the exposed axes, whereas the improvement in orientation discrimination at the attended location exhibits only weak transfer to complex stimuli. These results indicate that sensory adaptation by passive stimulus exposure should be viewed as a form of perceptual learning that is complementary to practice-based learning in that it reduces constraints on generalization.
Vision Research, 2010
Studies of perceptual learning have focused on aspects of learning that are related to early stages of sensory processing. However, conclusions that perceptual learning results in low-level sensory plasticity are controversial, since such learning may also be attributed to plasticity in later stages of sensory processing or in readout from sensory to decision stages, or to changes in high-level central processing. To address this controversy, we developed a novel random dot motion (RDM) stimulus to target motion cells selective to contrast polarity by ensuring the motion direction information arises only from signal dot onsets and not their offsets, and used these stimuli in the paradigm of task-irrelevant perceptual learning (TIPL). In TIPL, learning is achieved in response to a stimulus by subliminally pairing that stimulus with the targets of an unrelated training task. In this manner, we are able to probe learning for an aspect of motion processing thought to be a function of directional V1 simple cells with a learning procedure that dissociates the learned stimulus from the decision processes relevant to the training task. Our results show direction-selective learning for the designated contrast polarity that does not transfer to the opposite contrast polarity. This polarity specificity was replicated in a double training procedure in which subjects were additionally exposed to the opposite polarity. Taken together, these results suggest that TIPL for motion stimuli may occur at the stage of directional V1 simple cells. Finally, a theoretical explanation is provided to understand the data.
Perceptual Learning Reconfigures the Effects of Visual Adaptation
Journal of Neuroscience, 2012
Our sensory experiences over a range of different timescales shape our perception of the environment. Two particularly striking shortterm forms of plasticity with manifestly different time courses and perceptual consequences are those caused by visual adaptation and perceptual learning. Although conventionally treated as distinct forms of experience-dependent plasticity, their neural mechanisms and perceptual consequences have become increasingly blurred, raising the possibility that they might interact. To optimize our chances of finding a functionally meaningful interaction between learning and adaptation, we examined in humans the perceptual consequences of learning a fine discrimination task while adapting the neurons that carry most information for performing this task. Learning improved discriminative accuracy to a level that ultimately surpassed that in an unadapted state. This remarkable improvement came at a price: adapting directions that before learning had little effect elevated discrimination thresholds afterward. The improvements in discriminative accuracy grew quickly and surpassed unadapted levels within the first few training sessions, whereas the deterioration in discriminative accuracy had a different time course. This learned reconfiguration of adapted discriminative accuracy occurred without a concomitant change to the characteristic perceptual biases induced by adaptation, suggesting that the system was still in an adapted state. Our results point to a functionally meaningful push-pull interaction between learning and adaptation in which a gain in sensitivity in one adapted state is balanced by a loss of sensitivity in other adapted states.
Perceptual learning selectively refines orientation representations in early visual cortex
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2012
Although practice has long been known to improve perceptual performance, the neural basis of this improvement in humans remains unclear. Using fMRI in conjunction with a novel signal detection-based analysis, we show that extensive practice selectively enhances the neural representation of trained orientations in the human visual cortex. Twelve observers practiced discriminating small changes in the orientation of a laterally presented grating over 20 or more daily one-hour training sessions. Training on average led to a two-fold improvement in discrimination sensitivity, specific to the trained orientation and the trained location, with minimal improvement found for untrained orthogonal orientations or for orientations presented in the untrained hemifield. We measured the strength of orientation-selective responses in individual voxels in early visual areas (V1-V4) using signal detection measures, both pre-and post-training. Although the overall amplitude of the BOLD response was no greater after training, practice nonetheless specifically enhanced the neural representation of the trained orientation at the trained location. This training-specific enhancement of orientation-selective responses was observed in the primary visual cortex (V1) as well as higher extrastriate visual areas V2-V4, and moreover, reliably predicted individual differences in the behavioral effects of perceptual learning. These results demonstrate that extensive training can lead to targeted functional reorganization of the human visual cortex, refining the cortical representation of behaviorally relevant information.
Perceptual Learning in the Absence of Task or Stimulus Specificity
PLoS ONE, 2007
Performance on most sensory tasks improves with practice. When making particularly challenging sensory judgments, perceptual improvements in performance are tightly coupled to the trained task and stimulus configuration. The form of this specificity is believed to provide a strong indication of which neurons are solving the task or encoding the learned stimulus. Here we systematically decouple task-and stimulus-mediated components of trained improvements in perceptual performance and show that neither provides an adequate description of the learning process. Twenty-four human subjects trained on a unique combination of task (three-element alignment or bisection) and stimulus configuration (vertical or horizontal orientation). Before and after training, we measured subjects' performance on all four task-configuration combinations. What we demonstrate for the first time is that learning does actually transfer across both task and configuration provided there is a common spatial axis to the judgment. The critical factor underlying the transfer of learning effects is not the task or stimulus arrangements themselves, but rather the recruitment of commons sets of neurons most informative for making each perceptual judgment.
Learning perceptual skills: behavioral probes into adult cortical plasticity
Current Opinion in Neurobiology, 1997
Recent studies of the improvement of perceptual performance as a function of training-perceptual learning -have provided new insights into the neuronal substrates of this type of skill learning in the adult brain. Issues such as where in the brain, when and under what conditions practice-related changes occur are under investigation. The results of these studies suggest that a behaviorally relevant degree of plasticity is retained in the adult cortex, even within early, low-level representations in sensory and motor processing streams. The acquisition and retention of skills may share many characteristics with the functional plasticity subserving early-life learning and development. While the specificity of learning provides localization constraints, an important clue to the nature of the underlying neuronal changes is the time course of learning. Addresses Abbreviation PET positron emission tomography Poggio T, Fahle M, Edelman S: Fast perceptual learning in visual hyperacuity. Science 1992, 256:1018-l 021. Aronson L, Rosenhouse J, Podoshin L, Rosenhouse G, Zanutto SB: Pitch perception in patients with a multi-channel cochlear implant using various pulses width. Med Prog Technol 1994, 20~43-51. Dudai Y: Consolidation: fragility on the road to the engram. Neuron 1996, 17~367-370. Mollon JD, Danilova MV: Three remarks on perceptual learning. Spat Vis 1996, IO:51 -58. Saarinen J, Levi DM: Perceptual learning in vernier acuity: what is learned? Vision Res 1995, 35:519-527. Recanzone GH, Jenkins WM, Hradek GT, Merzenich MM: Progressive improvement in discriminative abilities in adult owl monkeys performing a tactile frequency discrimination task. J Neurophysiol 1992, 67:1015-l 030. Recanzone GH, Merzenich MM, Jenkins WM, Grajski KA, Dinse HR: Topographic reorganization of the hand representation in cortical area 3b owl monkeys trained in a frequency-discrimination task. J Neorophysiol 1992, 67:1031-1056. Recanzone GH, Merzenich MM, Jenkins WM: Frequency discrimination training engaging a restricted skin surface results in an emergence of a cutaneous response zone in cortical area 3a. J Neurophysiol 1992, 67:1057-l 070. Recanzone GH, Merzenich MM, Schreiner CE: Changes in the distributed temporal response properties of SI cortical neurons reflect improvements in performance on a temporally based tactile discrimination task. J Neurophysiol 1992, 67:1071-1091. Recanzone GH, Schreiner CE, Merzenich MM: Plasticity in the frequency representation of primary auditory cortex following discrimination training in adult owl monkeys. J Neurosci 1993, 13:87-l 03. Singer W: Development and plasticity of cortical processing architectures. Science 1995, 270~758-764.
Perceptual learning retunes the perceptual template in foveal orientation identification
Journal of Vision, 2004
What is learned during perceptual learning? We address this question by analyzing how perceptual inefficiencies improve over the course of perceptual learning (Dosher & Lu, 1998). Systematic measurements of human performance as a function of both the amount of external noise added to the signal stimulus and the length of training received by the observers enable us to track changes of the characteristics of the perceptual system (e.g., internal noise[s] and efficiency of the perceptual template) as perceptual learning progresses, and, therefore, identifies the mechanism(s) underlying the observed performance improvements. Two different observer models, the linear amplifier model (LAM) and the perceptual template model (PTM), however, have led to two very different theories of learning mechanisms. Here we demonstrate the failure of an LAM-based prediction-that the magnitude of learning-induced threshold reduction in high external noise must be less or equal to that in low external noise. In Experiment 1, perceptual learning of Gabor orientation identification in fovea showed substantial performance improvements only in high external noise but not in zero or low noise. The LAMbased model was "forced" to account for the data with a combination of improved calculation efficiency and (paradoxical) compensatory increases of the equivalent internal noise. Based on the PTM framework, we conclude that perceptual learning in this task involved learning how to better exclude external noise, reflecting retuning of the perceptual template. The data provide the first empirical demonstration of an isolable mechanism of perceptual learning. This learning completely transferred to a different visual scale in a second experiment.
Vision Research, 2006
Perceptual learning is an improvement in perceptual task performance reflecting plasticity in the perceptual system. Practice effects were studied in two object orientation tasks: a first order, luminance object task and a second-order, texture object task. Perceptual learning was small or absent in the first-order task, but consistently occurred for the second-order (texture) task, where it was limited to improvements in low external noise conditions, or stimulus enhancement [Dosher, B., & Lu, Z.-L. (1998). Perceptual learning reflects external noise filtering and internal noise reduction through channel reweighting.
Task specific disruption of perceptual learning
Journal of Vision, 2005
For more than a century, the process of stabilization has been a central issue in the research of learning and memory. Namely, after a skill or memory is acquired, it must be consolidated before it becomes resistant to disruption by subsequent learning. Although it is clear that there are many cases in which learning can be disrupted, it is unclear when learning something new disrupts what has already been learned. Herein, we provide two answers to this question with the demonstration that perceptual learning of a visual stimulus disrupts or interferes with the consolidation of a previously learned visual stimulus. In this study, we trained subjects on two different hyperacuity tasks and determined whether learning of the second task disrupted that of the first. We first show that disruption of learning occurs between visual stimuli presented at the same orientation in the same retinotopic location but not for the same stimuli presented at retinotopically disparate locations or different orientations at the same location. Second, we show that disruption from stimuli in the same retinotopic location is ameliorated if the subjects wait for 1 h before training on the second task. These results indicate that disruption, at least in visual learning, is specific to features of the tasks and that a temporal delay of 1 h can stabilize visual learning. This research shows that visual learning is susceptible to disruption and elucidates the processes by which the brain can consolidate learning and thus protect what is learned from being overwritten.
What we see changes how we see : analyzing the plasticity of the horizontal effect
The relationship between the processing of orientations by the human visual system has been related to the orientation content of the natural environment; horizontal orientations, while predominant in natural environments, are perceived less well than vertical and oblique orientations are perceived best, though they are least prevalent in the natural world. This 'horizontal effect' has further extended the well-studied relationship between visual encoding and natural scene statistics as the differential perception of orientations in broadband scenes inversely matches their differential representation in the natural environment. However, the original hypothesis that this relationship may have evolved across millennia in order to make the visual system an efficient informationtransmitting system has been called into question by research showing the modification of orientation perception by exposure to altered environments and studies showing a later development of adult-like orientation processing. Recent work into the effects of adaptation on visual encoding of the natural environment have led me to the conclusion that the relationship between the statistics of the natural world and visual encoding is, in a way, much simpler than previously posited; rather than being adapted over millennia to whiten the typical natural scene anisotropy, the visual system adjusts processing v dynamically to match the current visual environment. The project presented here details how the statistics of the recently viewed environment affect the way that the visual brain processes information. To assess the effect of recent exposure on broadband orientation processing, the orientation content subjects viewed was modified via fast Fourier transform (FFT) filtering of their environment in near-real-time. Results show that experience in an altered environment modifies anisotropic processing: observers' orientation perception changes from matching the typical environmental distribution to matching that of the recently experienced atypical environment. The results of these experiments can be predicted by assuming that observers' biases of perception are probabilistic and rely on an internal model that matches the recently experienced environmental distribution. This change in perception indicates not only that orientation processing is plastic, but that it is related in a predictable way to an observer's recent visual environment. vi