A pet study of human skill learning: changes in brain activity related to learning an orientation discrimination task

Informational feedback accelerates learning in multi-alternative perceptual judgements of orientation

Experience or training can substantially improve perceptual performance through perceptual learning, and the extent and rate of these improvements may be affected by feedback. In this paper, we first developed a neural network model based on the integrated reweighting theory (Dosher et al., 2013) to account for perceptual learning and performance in n-alternative identification tasks and the dependence of learning on different forms of feedback. We then report an experiment comparing the effectiveness of response feedback (RF) versus accuracy feedback (AF) or no feedback (NF) (full versus partial versus no supervision) in learning a challenging eight-alternative visual orientation identification (8AFC) task. Although learning sometimes occurred in the absence of feedback (NF), RF had a clear advantage above AF or NF in this task. Using hybrid supervision learning rules, a new n-alternative identification integrated reweighting theory (I-IRT) explained both the differences in learning curves given different feedback and the dynamic changes in identification confusion data. This study shows that training with more informational feedback (RF) is more effective, though not necessary, in these challenging n-alternative tasks, a result that has implications for developing training paradigms in realistic tasks.

Changes in brain perfusion with training-related visuomotor improvement in MS

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system. A better understanding of the mechanisms supporting brain plasticity in MS would help to develop targeted interventions to promote recovery. A total of 29 MS patients and 19 healthy volunteers underwent clinical assessment and multi-modal MRI acquisition [fMRI during serial reaction time task (SRT), DWI, T1w structural scans and ASL of resting perfusion] at baseline and after 4-weeks of SRT training. Reduction of functional hyperactivation was observed in MS patients following the training, shown by the stronger reduction of the BOLD response during task execution compared to healthy volunteers. The functional reorganization was accompanied by a positive correlation between improvements in task accuracy and the change in resting perfusion after 4 weeks' training in right angular and supramarginal gyri in MS patients. No longitudinal changes in WM and GM measures and no correlation between task performance improvements and brain structure were observed in MS patients. Our results highlight a potential role for CBF as an early marker of plasticity, in terms of functional (cortical reorganization) and behavioral (performance improvement) changes in MS patients that may help to guide future interventions that exploit preserved plasticity mechanisms.

Tactile-to-Visual Cross-Modal Transfer of Texture Categorisation Following Training: An fMRI Study

We investigated the neural underpinnings of texture categorisation using exemplars that were previously learned either within modalities (visual training and visual test) or across modalities (tactile training and visual test). Previous models of learning suggest a decrease in activation in brain regions that are typically involved in cognitive control during task acquisition, but a concomitant increase in activation in brain regions associated with the representation of the acquired information. In our study, participants were required to learn to categorise fabrics of different textures as either natural or synthetic. Training occurred over several sessions, with each fabric presented either visually or through touch to a participant. Pre- and post-training tests, in which participants categorised visual images only of the fabrics, were conducted during a functional magnetic resonance imaging (fMRI) scan. Consistent with previous research on cognitive processes involved in task acquisition, we found that categorisation training was associated with a decrease in activation in brain regions associated with cognitive systems involved in learning, including the superior parietal cortex, dorsal anterior cingulate cortex (dACC), and the right dorsolateral prefrontal cortex (DLFC). Moreover, these decreases were independent of training modality. In contrast, we found greater activation to visual textures in a region within the left medial occipital cortex (MOC) following training. There was no overall evidence of an effect of training modality in the main analyses, with texture-specific regional changes associated with both within- (visual) and cross- (touch) modal training. However, further analyses suggested that, unlike categorisation performance following within-modal training, crossmodal training was associated with bilateral activation of the MOC. Our results support previous evidence for a multisensory representation of texture within early visual regions of the cortex and provide insight into how multisensory categories are formed in the brain.

Effects of regular aerobic exercise on visual perceptual learning

This study investigated the influence of five days of moderate intensity aerobic exercise on the acquisition and consolidation of visual perceptual learning using a motion direction discrimination (MDD) task. The timing of exercise relative to learning was manipulated by administering exercise either before or after perceptual training. Within a matched-subjects design, twenty-seven healthy participants (n = 9 per group) completed five consecutive days of perceptual training on a MDD task under one of three interventions: no exercise, exercise before the MDD task, or exercise after the MDD task. MDD task accuracy improved in all groups over the five-day period, but there was a trend for impaired learning when exercise was performed before visual perceptual training. MDD task accuracy (mean ± SD) increased in exercise before by 4.5 ± 6.5%; exercise after by 11.8 ± 6.4%; and no exercise by 11.3 ± 7.2%. All intervention groups displayed similar MDD threshold reductions for the trained and untrained motion axes after training. These findings suggest that moderate daily exercise does not enhance the rate of visual perceptual learning for an MDD task or the transfer of learning to an untrained motion axis. Furthermore, exercise performed immediately prior to a visual perceptual learning task may impair learning. Further research with larger groups is required in order to better understand these effects.

Fluoxetine Does Not Enhance Visual Perceptual Learning and Triazolam Specifically Impairs Learning Transfer

The selective serotonin reuptake inhibitor fluoxetine significantly enhances adult visual cortex plasticity within the rat. This effect is related to decreased gamma-aminobutyric acid (GABA) mediated inhibition and identifies fluoxetine as a potential agent for enhancing plasticity in the adult human brain. We tested the hypothesis that fluoxetine would enhance visual perceptual learning of a motion direction discrimination (MDD) task in humans. We also investigated (1) the effect of fluoxetine on visual and motor cortex excitability and (2) the impact of increased GABA mediated inhibition following a single dose of triazolam on post-training MDD task performance. Within a double blind, placebo controlled design, 20 healthy adult participants completed a 19-day course of fluoxetine (n = 10, 20 mg per day) or placebo (n = 10). Participants were trained on the MDD task over the final 5 days of fluoxetine administration. Accuracy for the trained MDD stimulus and an untrained MDD stimulus configuration was assessed before and after training, after triazolam and 1 week after triazolam. Motor and visual cortex excitability were measured using transcranial magnetic stimulation. Fluoxetine did not enhance the magnitude or rate of perceptual learning and full transfer of learning to the untrained stimulus was observed for both groups. After training was complete, trazolam had no effect on trained task performance but significantly impaired untrained task performance. No consistent effects of fluoxetine on cortical excitability were observed. The results do not support the hypothesis that fluoxetine can enhance learning in humans. However, the specific effect of triazolam on MDD task performance for the untrained stimulus suggests that learning and learning transfer rely on dissociable neural mechanisms.

Evidence for corticostriatal dysfunction during cognitive skill learning in adolescent siblings of patients with childhood-onset schizophrenia

Patients with schizophrenia perform poorly on cognitive skill learning tasks. This study is the first to investigate the neural basis of impairment in cognitive skill learning in first-degree adolescent relatives of patients with schizophrenia. We used functional magnetic resonance imaging to compare activation in 16 adolescent siblings of patients with childhood-onset schizophrenia (COS) and 45 adolescent controls to determine whether impaired cognitive skill learning in individuals with genetic risk for schizophrenia was associated with specific patterns of neural activation. The siblings of patients with COS were severely impaired on the Weather Prediction Task (WPT) and showed a relative deactivation in frontal regions and in the striatum after extensive training on the WPT compared with controls. These differences were not accounted for by performance differences in the 2 groups. The results suggest that corticostriatal dysfunction may be part of the liability for schizophrenia.

Perceptual learning of motion direction discrimination with suppressed and unsuppressed MT in humans: an fMRI study

The middle temporal area of the extrastriate visual cortex (area MT) is integral to motion perception and is thought to play a key role in the perceptual learning of motion tasks. We have previously found, however, that perceptual learning of a motion discrimination task is possible even when the training stimulus contains locally balanced, motion opponent signals that putatively suppress the response of MT. Assuming at least partial suppression of MT, possible explanations for this learning are that 1) training made MT more responsive by reducing motion opponency, 2) MT remained suppressed and alternative visual areas such as V1 enabled learning and/or 3) suppression of MT increased with training, possibly to reduce noise. Here we used fMRI to test these possibilities. We first confirmed that the motion opponent stimulus did indeed suppress the BOLD response within hMT+ compared to an almost identical stimulus without locally balanced motion signals. We then trained participants on motion opponent or non-opponent stimuli. Training with the motion opponent stimulus reduced the BOLD response within hMT+ and greater reductions in BOLD response were correlated with greater amounts of learning. The opposite relationship between BOLD and behaviour was found at V1 for the group trained on the motion-opponent stimulus and at both V1 and hMT+ for the group trained on the non-opponent motion stimulus. As the average response of many cells within MT to motion opponent stimuli is the same as their response to non-directional flickering noise, the reduced activation of hMT+ after training may reflect noise reduction.

Neural correlates of contextual cueing are modulated by explicit learning

Contextual cueing refers to the facilitated ability to locate a particular visual element in a scene due to prior exposure to the same scene. This facilitation is thought to reflect implicit learning, as it typically occurs without the observer's knowledge that scenes repeat. Unlike most other implicit learning effects, contextual cueing can be impaired following damage to the medial temporal lobe. Here we investigated neural correlates of contextual cueing and explicit scene memory in two participant groups. Only one group was explicitly instructed about scene repetition. Participants viewed a sequence of complex scenes that depicted a landscape with five abstract geometric objects. Superimposed on each object was a letter T or L rotated left or right by 90°. Participants responded according to the target letter (T) orientation. Responses were highly accurate for all scenes. Response speeds were faster for repeated versus novel scenes. The magnitude of this contextual cueing did not differ between the two groups. Also, in both groups repeated scenes yielded reduced hemodynamic activation compared with novel scenes in several regions involved in visual perception and attention, and reductions in some of these areas were correlated with response-time facilitation. In the group given instructions about scene repetition, recognition memory for scenes was superior and was accompanied by medial temporal and more anterior activation. Thus, strategic factors can promote explicit memorization of visual scene information, which appears to engage additional neural processing beyond what is required for implicit learning of object configurations and target locations in a scene.

An influence of amplitude modulation on interaural level difference processing suggested by learning patterns of human adults

Humans rely on interaural level differences (ILDs) to determine the location of sound sources, particularly for high-frequency sounds. Previously, ILD-discrimination performance with a 4-kHz pure tone was reported to improve with multi-hour training. Here the effect of the same training regimen on ILD discrimination with a 4-kHz tone sinusoidally amplitude modulated (SAM) at 0.3 kHz was examined. Ten of the 16 trained listeners improved more than untrained controls, demonstrating training-induced learning. However, compared to the learning previously obtained with the 4-kHz pure tone, learning with the SAM tone was less predictable based on starting performance, took longer to complete, and was characterized by specificity to stimulus type (SAM vs pure tones) rather than stimulus frequency. These differences demonstrate an influence of amplitude modulation on learning of ILD discrimination. This influence suggests that the auditory system makes use of amplitude envelope information in determining ILD-discrimination performance, a form of interaction between time and level processing in the binaural system.

The neural substrates of visual perceptual learning of words: implications for the visual word form area hypothesis

Abstract It remains under debate whether the fusiform visual word form area (VWFA) is specific to visual word form and whether visual expertise increases its sensitivity (Xue et al., 2006; Cohen et al., 2002). The present study examined three related issues: (1) whether the VWFA is also involved in processing foreign writing that significantly differs from the native one, (2) the effect of visual word form training on VWFA activation after controlling the task difficulty, and (3) the transfer of visual word form learning. Eleven native English speakers were trained, during five sessions, to judge whether two subsequently flashed (100-msec duration with 200-msec interval) foreign characters (i.e., Korean Hangul) were identical or not. Visual noise was added to the stimuli to manipulate task difficulty. In functional magnetic resonance imaging scans before and after training, subjects performed the task once with the same noise level (i.e., parameter-matched scan) and once with noise level changed to match performance from pretraining to posttraining (i.e., performance-matched scan). Results indicated that training increased the accuracy in parameter-matched condition but remained constant in performance-matched condition (because of increasing task difficulty). Pretraining scans revealed stronger activation for English words than for Korean characters in the left inferior temporal gyrus and the left inferior frontal cortex, but not in the VWFA. Visual word form training significantly decreased the activation in the bilateral middle and left posterior fusiform when either parameters or performance were matched and for both trained and new items. These results confirm our conjecture that the VWFA is not dedicated to words, and visual expertise acquired with training reduces rather than increases its activity.

Neural systems for perceptual skill learning

Recent studies have begun to use functional neuroimaging techniques to examine the changes in brain activity that occur as humans learn new skills. This review outlines results from a number of imaging studies examining visual perceptual skill learning. Although the regions engaged during skill learning differ across tasks, a common finding has been increasing activation in the inferior temporal and fusiform gyri as skill is acquired and activation of the caudate nucleus in association with learning. Neuroimaging has great promise for the understanding of learning at the level of large neural populations, but further work is necessary to understand the specificity of learning-related changes and their relation to underlying neurophysiological plasticity.

Language experience shapes fusiform activation when processing a logographic artificial language: An fMRI training study

The significant role of the left midfusiform cortex in reading found in recent neuroimaging studies has led to the visual word form area (VWFA) hypothesis. This hypothesis suggests that years of experience reading native language change the visual expertise of this region to be especially sensitive to the visual form of native language. The present study aimed at testing this hypothesis by exploring the role of language experience in shaping the fusiform activation. We designed a logographic artificial language (LAL) using the visual form and pronunciation of Korean Hangul characters (but their correspondence was shuffled) and assigning arbitrary meanings to these characters. Twelve native Chinese Mandarin speakers (6 male and 6 female, 18 to 21 years old) with no prior knowledge of Korean language were trained in the visual form of these characters for 2 weeks, followed by 2 weeks each of phonological and semantic training. Behavioral data indicated that training was effective in increasing the efficiency of visual form processing and establishing the connections among visual form, sounds, and meanings. Imaging data indicated that at the pre-training stage, subjects showed stronger activation in the fusiform regions for LAL than for Chinese across both one-back visual matching task and the passive viewing task. Visual form training significantly decreased the activation of bilateral fusiform cortex and the left inferior occipital cortex, whereas phonological training increased activation in these regions, and the right fusiform remained more active after semantic training. Increased activations after phonological and semantic training were also evident in other regions involved in language processing. These findings thus do not seem to be consistent with the visual-expertise-induced-sensitivity hypothesis about fusiform regions. Instead, our results suggest that visual familiarity, phonological processing, and semantic processing all make significant but different contributions to shaping the fusiform activation.

Category-specific organization of prefrontal response-facilitation during priming

Perceptual priming is a fundamental long-term memory capability that allows more efficient and faster responding to a stimulus as a result of prior exposure to that stimulus. The two major components of priming are facilitated response expression and improved stimulus identification. Recent fMRI studies have identified a potential neural correlate for response-facilitation, namely the repetition-related activity decrements in prefrontal cortex that are linearly correlated with improvements in reaction times. However, the neural processes underlying such response-facilitation are still unclear. They could be stimulus-selective stimulus-response mapping processes or general response-learning mechanisms. In human imaging studies, behavioral priming has been associated with decreased hemodynamic responses in prefrontal cortex and in category-specific brain regions of the ventral visual stream. Currently, it is unclear whether priming-related response decreases in prefrontal cortex are also category-specific. In this fMRI study, 16 subjects performed a repetition priming task employing category-specific identification judgments on pictures of faces (male/female judgment), scenes (indoor/outdoor judgment) and scrambled 'noise' pictures (simple button press). The repeated faces and scenes were identified faster than first presentations indicating priming. Hemodynamic decreases for repetitions were observed in a left inferior (near Brodman Area, BA, 44) and middle frontal (BA8) region of the prefrontal cortex, in category-specific areas of the ventral stream (bilateral fusiform face area, FFA, parahippocampal place area, PPA), and two category-specific right lateral occipital (LOC) regions. Hemodynamic increases for repetitions appeared in the caudate and cerebellum. However, the prefrontal areas were the only regions that showed a correlation between repetition-related reaction time improvement and hemodynamic decrease. Importantly, the correlations were category-specific in their relationship to reaction time improvement: in the left inferior frontal cortex the correlations were specific for scenes whereas and in left middle frontal gyrus they were specific for faces. There were no correlations between behavior and repetition suppression for both LOC regions, FFA and PPA. These data reveal that response-facilitation in prefrontal cortex is organized according to stimulus-properties, compatible with learning of stimulus-response mapping rather than response learning in general.

Learning and retention of movement sequences in Parkinson's disease

The purpose of this study was to examine motor learning and retention given extensive practice in two fundamentally different movement sequences. One sequence was a memory-driven task (performing a series of whole body positions from memory) and the other a context-driven task (buttoning). Practice took place over 3 weeks, with performance measured weekly; retention was measured weekly for 3 weeks after practice. There were 7 people with Parkinson's disease (PD) and 7 age-matched neurologically healthy people who participated in this study. Both groups improved performance on both tasks with practice, with the majority of the change for the PD group occurring between 1 and 2 weeks of practice. Although those with PD did not necessarily perform as well as age-matched controls, they learned both sequences in a manner similar to age-matched controls, and exhibited retention across the 3-week retention interval. If people with PD are given sufficient practice they can learn and retain both memory-based and context-driven movement sequences as well as age-matched controls. The results provide support for maintaining physical activity and for intervention through movement therapy.

Functional activation imaging in aging and dementia

With life expectancy increasing continuously, the effects of neurodegeneration on brain function are a topic of ever increasing importance. Thus there is a need for tools and models that probe both the functional consequences of neurodegenerative processes and compensatory mechanisms that might occur. As neurodegenerative burden and compensatory mechanisms may change over time, these tools will ideally be applied multiple times over the lifespan. Specifically, in order to elucidate whether brain-activation patterns in Alzheimer's disease (AD) and in healthy aging follow general rules in the context of degeneration and compensation, it is necessary to compare functional brain-activation patterns during different states of neurodegeneration. This article integrates the findings of functional activation studies at different stages of neurodegeneration: in healthy aging, in subjects at high risk of developing dementia, in subjects with mild cognitive impairment (MCI), and in patients suffering from AD. We review existing theoretical models that aim to explain the underlying mechanisms of functional activation changes in aging and dementia, and we propose an integrative account, which allows for different neural response patterns depending on the amount of neuronal damage and the recruitment of compensatory pathways.

Neural changes in the ventral and dorsal visual streams during pattern recognition learning

The learning process related to pattern and object recognition is difficult to study because the human brain has a remarkable capacity to recognise complex visual forms from early infancy. In the present study, we investigated on-going neural changes underlying the learning process of visual pattern recognition by means of a device substituting audition for vision. Functional MRI evidenced the gradual pattern recognition-induced recruitment of the ventral visual stream, bilaterally, from learning session 1 to session 3, and a slight decrease in these activation foci from session 3 to session 4. The initial increase in activation is thought to reflect the gradually enhanced visualisation of patterns in the subjects' mind across sessions. By contrast the subsequent decrease reported at the end of the training period is interpreted as the progressive optimisation of neuronal responses elicited by the task. Our results, in accordance with previous observations, suggest that the succession of activation increase and decrease in sensori-motor areas could be a general rule in sensory and sensori-motor learning.

Human Functional Neuroimaging of Brain Changes Associated with Practice

The discovery that experience-driven changes in the human brain can occur from a neural to a cortical level throughout the lifespan has stimulated a proliferation of research into how neural function changes in response to experience, enabled by neuroimaging methods such as positron emission tomography and functional magnetic resonance imaging. Studies attempt to characterize these changes by examining how practice on a task affects the functional anatomy underlying performance. Results are incongruous, including patterns of increases, decreases and functional reorganization of regional activations. Following an extensive review of the practice-effects literature, we distinguish a number of factors affecting the pattern of practice effects observed, including the effects of task domain, changes at the level of behavioural and cognitive processes, the time-window of imaging and practice, and of a number of other influences and miscellaneous confounding factors. We make a novel distinction between patterns of reorganization and redistribution as effects of task practice on brain activation, and emphasize the need for careful attention to practice-related changes occurring on the behavioural, cognitive and neural levels of analysis. Finally, we suggest that functional and effective connectivity analyses may make important contributions to our understanding of changes in functional anatomy occurring as a result of practice on tasks.