Neurocomputing 38}40 (2001) 1217}1222 Stimulus optimisation in primary visual cortex Peter Fo K ldia H k School of Psychology, University of St, Andrews, St. Andrews, KY16 9JU, UK Abstract A computational method is introduced for "nding e!ective stimuli for sensory neurons. In single unit recording experiments, it maximises simultaneously recorded responses by changing stimuli along an estimated gradient with respect to stimuli. The estimate is the correlation between noise added to an evolving base stimulus and the response. Pixel optimisation for monkey V1 rapidly produces stimuli consistent with conventionally determined tuning even for complex cells. For the same complex cell, repeated runs of the optimisation gave solutions with di!erent phase. Unlike reverse correlation, this method is applicable to non-linear, context- sensitive cells, possibly also in higher sensory areas.  2001 Elsevier Science B.V. All rights reserved. Keywords: Stimulus optimisation; Response selectivity; V1; Non-linear optimisation 1. Introduction An important part of the functional description of a neuron in the sensory system is the identi"cation of the stimulus or class of stimuli that causes it to respond strongly. Searching for optimal or near-optimal stimuli is traditionally performed manually using a limited and predetermined set of stimuli. This is not easy even when the relevant parameters of the stimulus tuning are assumed to be known, as in the case of primary visual cortex. The response is noisy, it is tuned to several parameters, and the response E-mail address: peter.foldiak@st-andrews.ac.uk (P. Fo K ldia H k).  Partially supported by the BBSRC, UK. The experiments described here were carried out on a research leave at the Center for Neural Science at New York University in the laboratory of J. Anthony Movshon. I am grateful to Tony and other members of the Center, especially Wyeth Bair, Matthew Smith, James Cavanaugh and Najib Majaj, who gave me substantial help in adapting the program to the software and hardware in the lab, and who carried out the physiological parts of the experiments. 0925-2312/01/$-see front matter  2001 Elsevier Science B.V. All rights reserved. PII:S0925-2312(01)00570-7