Psychophysics as a tool to investigate the visual system

Abstract

The psychophysical method contributes to the study of the visual system a black-box analysis of the (human) brain by investigating input-output relations, i.e., the behaviorally relevant results of processing a wide variety of sensory stimuli. Visual and auditory stimuli provide very versatile inputs and, usually, detection or discrimination thresholds are determined in order to measure the processing capabilities of the (central) nervous system. Today, a sort of ‘gray-box’ analysis is possible by combining the methods of classical psychophysics with those of anatomy, histology, single-cell recordings in animals, recordings of the sum potentials that accompany the function of the brain (EEG, MEG), recording changes in local cerebral blood flow during specific tasks (PET, fMRI), and studies of patients suffering from circumscribed brain lesions. While a complete analysis of brain function is impossible with the methods of psychophysics due mainly to the nonlinearities of the system, a fair amount of knowledge can be gained and adequate models of special aspects of brain function developed based on psychophysical results. Moreover, psychphysics is an ideal method to study adaptation and (perceptual) learning in humans, proving the astonishing plasticity of most if not all cortical areas even in adults.