Journal of Neuroscience Methods 114 (2002) 51 – 61 PC-based visual stimuli for behavioural and electrophysiological studies of optic flow field detection Aaron P. Johnson a, *, B. Geoff Horseman a , Martin W.S. Macauley b , W. Jon P. Barnes a a Diision of Enironmental and Eolutionary Biology, Institute of Biomedical and Life Sciences, Graham Kerr Building, Uniersity of Glasgow, Glasgow G12 8QQ, Scotland, UK b Department of Electronics and Electrical Engineering, Uniersity of Glasgow, Glasgow G12 8QQ, Scotland, UK Received 31 August 2001; received in revised form 31 October 2001; accepted 1 November 2001 Abstract 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°. 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. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Vision; Visual stimuli; Computer graphics; Crab; Carcinus maenas ; Optic flow field www.elsevier.com/locate/jneumeth 1. Introduction Optic flow, the pattern of global image motion over the retina resulting from an animal moving through its surroundings (Gibson, 1950, 1966), contains valuable cues to direction and speed of motion, and the layout of objects in the environment (Sobey and Srinivasan, 1991). Most of this information is encoded within the translational component of optic flow, which has a focus of expansion in the direction of heading, and cues to the distance of objects. By comparison, the rota- tional component of optic flow generated by the ani- mal’s turning is less informative, although it can be used to detect deviations from a straight path. Most animals with good vision remove the rotational compo- nent, using compensatory movements of the eyes or head, thereby extracting the information-rich transla- tional flow (see reviews by Land, 1995, 1999). Recently, much interest has focussed on how the rotational and translational components are separated from each other, and how optic flow is processed at the neuronal level. There is now compelling evidence from a range of species that this process involves large-field motion-sen- sitive neurones tuned to behaviourally relevant optic flow patterns (for reviews see Albright, 1993; Hausen, 1993; Krapp, 2000). Our aim has been to extend this type of study to crustaceans, specifically land and shore crabs, which show strong compensatory eye movements to rotational flow field stimuli (Barnes, 1990; Barnes and Nalbach, 1993; Kern et al., 1993; Nalbach et al., 1993; Blanke et al., 1997). In order to do this, we required a flexible visual stimulation system that could deliver both global and * Corresponding author. Tel.: +44-141-3304-430; fax: +44-141- 3305-971. E-mail address: a.johnson@elec.gla.ac.uk (A.P. Johnson). 0165-0270/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0165-0270(01)00508-8