PC-based visual stimuli for behavioural and electrophysiological studies of optic flow field detection

A PC-based visual-stimulus-generation package for behavioural and electrophysiological studies of responses to optic flow is described. Developed for studies of crab vision, the package is particularly well suited for use with animals that have very large fields of view, i.e. +/-120 degrees. Programs, written in the Borland Delphi language, use the OpenGL graphics library to create realistic representations of motion in a three dimensional environment. Large-field stimuli include simulations of self-motion (rotation and translation, separately or in combination) relative to a square-wave grating or other, user-selected, background. The package also includes representations of approaching and receding objects, and rotating spiral patterns for the investigation of neural responses to looming/anti-looming. Additionally, the package provides local motion stimuli, translating or rotating targets presented at many points in the receptive field, which can be used to derive response maps of large-field motion-sensitive interneurones. In all these stimuli, inconsistencies in animation timing that have hitherto hindered the use of standard PCs running Microsoft Windows for such applications have been minimised by using an improved real-time clock to control the animation cycle.