Spatial properties of dark- and light-adapted visual fields of butterfly interneurones

Abstract

Visual fields of protocerebral interneurones in butterflies in response to white, punctate flashes were recorded to obtain quantitative information about changes in field size and structure during light adaptation. The average width of restricted fields is reduced from 50-32°, the average height from 51-25 (Fig. 4). An adaptation index, relating changes in response density to the reduction in field area demonstrates three types of behaviour during light adaptation: (a) fields which get very diffuse, (b) fields with no major structural changes and (c) fields with a concentration of their densely responding area, losing diffuse regions (Figs. 4e and 5). Smaller visual fields are concentrated in the lower frontal part of the butterfly's field of vision, which is represented most extensively in the insect visual system (Fig. 6). The possible functional significance of the findings is discussed with respect to pattern vision, tracking, and fixation. It is suggested that the large field (probably movement detecting) neurones are involved in course control and stabilization, whereas small field neurones are specialized for detection and identification of small objects.