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NJIT Mathematical Biology Seminar

Tuesday, February 2, 2010, 2:30pm
Cullimore Hall 611
New Jersey Institute of Technology

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A model of two interacting accumulators for reach and saccade reaction time behavior

Daniel Marti

Center for Neural Sciences, New York University

During coordinated eye-hand movements, saccade and reach reaction times are correlated in both humans and monkeys. The relationship between reaction times and coordination can be explored systematically in dual reaction-time tasks, in which the degree of coordination between movements is manipulated by cuing the two responses at different times separated by some random interval, or stimulus onset asynchrony (SOA). In the first part of the talk I will report results of a dual-reaction time study with monkeys. The study shows that correlations of saccade and reach reaction times are high and positive at short SOAs, and that these correlations drop quickly as the SOA increases to a few hundred milliseconds. Furthermore, mean saccade reaction times decrease for short SOAs, suggesting a facilitation of saccades by reaches when they are cued nearly simultaneously. To gain insight into the functional mechanisms underlying eye-hand coordination, I will present a phenomenological model of reaction time based on two mutually coupled accumulators. Each accumulator is associated with one particular movement and triggers a response when it hits a prescribed threshold. The accumulator is ultimately thought to be encoded in the firing activity of a neuronal population involved in the planning of the associated movement. According to this view, the observed phenomenology of reaction times would reflect the interaction between effector-specific planning areas. I will consider several biologically plausible types of interaction and analyze the predicted behavioral outcome of each of them. The analysis shows that a model with mutual excitation and asymmetric coupling accounts best for the dependencies on SOA of the low-order moments of the reaction time distributions. This result suggests that correlations in reaction times may arise from reciprocal excitatory projections between planning areas.