Sensorimotor Decisions, Eye Movements, And Uncertainty

Kestutis Kveraga

Department of Brain and Cognitive Science,
Darmouth College

The ability to rapidly and accurately select the appropriate response from a set of response alternatives is an essential feature of adaptive behavior. It has become nearly axiomatic that it takes longer to select a response when the number of stimulus–response alternatives (‘S–R uncertainty’) is greater. This relationship is described by Hick’s law, which states that reaction times (RTs) increase in proportion to the logarithm of the number of S–R alternatives. However, we have shown (Kveraga et al., 2002) that the latencies of visually guided saccades exhibit no RT increases beyond the 1–alternative (simple reaction time) condition, thus violating a fundamental principle in sensorimotor decision–making. We hypothesized that this result is due to a one–to–one S–R mapping in the superior colliculus: visually guided saccades are selected automatically, using topographically organized pathways that convert spatially coded visual activity into spatially coded motor commands. I will discuss some hypotheses about how this highly efficient arrangement may have arisen, and will talk about the only other response modality we have found that is also immune to S–R uncertainty effects. I will go over a number of studies in which we examined other highly S–R compatible response modalities, studied cross–sectional and longitudinal learning, taxed the saccadic selection processes with attentional loads and near–threshold stimuli, and imaged the response selection processes with fMRI. I will end my talk with a brief overview of a different type of uncertainty and the paradigm I devised to study it: namely, uncertainty about the speed with which a sensorimotor decision has to be made (‘speed uncertainty’) and the performance shifts associated with it. This last line of research seeks to answer the following questions: 1) what effects does speed uncertainty have across a wide spectrum of performance speeds? 2) what are the behavioral and neural mechanisms that mediate these performance shifts?