Integrated Approaches to Perceptual Learning

Adaptation in the visual cortex: a case for probing neuronal populations with natural stimuli

The perception of, and neural responses to, sensory stimuli in the present are influenced by what has been observed in the past—a phenomenon known as adaptation. We focus on adaptation in visual cortical neurons as a paradigmatic example. We review recent work that represents two shifts in the way we study adaptation, namely (i) going beyond single neurons to study adaptation in populations of neurons and (ii) going beyond simple stimuli to study adaptation to natural stimuli. We suggest that efforts in these two directions, through a closer integration of experimental and modeling approaches, will enable a more complete understanding of cortical processing in natural environments.

Perceptual learning in Vision Research

Reports published in Vision Research during the late years of the 20th century described surprising effects of long-term sensitivity improvement with some basic visual tasks as a result of training. These improvements, found in adult human observers, were highly specific to simple visual features, such as location in the visual field, spatial-frequency, local and global orientation, and in some cases even the eye of origin. The results were interpreted as arising from the plasticity of sensory brain regions that display those features of specificity within their constituting neuronal subpopulations. A new view of the visual cortex has emerged, according to which a degree of plasticity is retained at adult age, allowing flexibility in acquiring new visual skills when the need arises. Although this "sensory plasticity" interpretation is often questioned, it is commonly believed that learning has access to detailed low-level visual representations residing within the visual cortex. More recent studies during the last decade revealed the conditions needed for learning and the conditions under which learning can be generalized across stimuli and tasks. The results are consistent with an account of perceptual learning according to which visual processing is remodeled by the brain, utilizing sensory information acquired during task performance. The stability of the visual system is viewed as an adaptation to a stable environment and instances of perceptual learning as a reaction of the brain to abrupt changes in the environment. Training on a restricted stimulus set may lead to perceptual overfitting and over-specificity. The systemic methodology developed for perceptual learning, and the accumulated knowledge, allows us to explore issues related to learning and memory in general, such as learning rules, reinforcement, memory consolidation, and neural rehabilitation. A persistent open question is the neuro-anatomical substrate underlying these learning effects.