LATER models of neural decision behavior in choice tasks

The time course of perceptual choice is discussed in a model of gradual, leaky, stochastic, and competitive information accumulation in nonlinear decision units. Special cases of the model match a classical diffusion process, but leakage and competition work together to address several challenges to existing diffusion, random walk, and accumulator models. The model accounts for data from choice tasks using both time-controlled (e.g., response signal) and standard reaction time paradigms and its adequacy compares favorably with other approaches. A new paradigm that controls the time of arrival of information supporting different choice alternatives provides further support. The model captures choice behavior regardless of the number of alternatives, accounting for the log-linear relation between reaction time and number of alternatives (Hick's law) and explains a complex pattern of visual and contextual priming in visual word identification. Show more

The latency between the appearance of a visual target and the start of the saccadic eye movement made to look at it varies from trial to trial to an extent that is inexplicable in terms of ordinary 'physiological' processes such as synaptic delays and conduction velocities. An alternative interpretation is that it represents the time needed to decide whether a target is in fact present: decision processes are necessarily stochastic, because they depend on extracting information from noisy sensory signals. In one such model, the presence of a target causes a signal in a decision unit to rise linearly at a rate r from its initial value s0 until it reaches a fixed threshold theta, when a saccade is initiated. One can regard this decision signal as a neural estimate of the log likelihood of the hypothesis that the target is present, the threshold being the significance criterion or likelihood level at which the target is presumed to be present. Experiments manipulating the prior probability of the target's appearing confirm this notion: the latency distribution then changes in the way expected if s0 simply reflects the prior log likelihood of the stimulus. Show more

This review focuses on eye movement control by the cerebral cortex, mainly in humans. Data have emerged based on the important contribution of recent techniques such as transcranial magnetic stimulation and functional magnetic resonance imaging, which provide complementary results to those of the classical lesion and electrical stimulation studies. The location of the human frontal eye field and its role in pursuit eye movement control were recently detailed. Cumulative evidence for the role of the dorsolateral prefrontal cortex in unwanted reflexive saccade inhibition, short-term spatial memory and prediction suggests that this area controls decisional processes governing ocular motor behaviour. The organization of spatial memory in the dorsolateral prefrontal cortex (short-term), the parahippocampal cortex (medium-term) and the hippocampal formation (long-term) is also reviewed with the results of recent transcranial magnetic stimulation studies. The relatively complicated anatomy of the posterior parietal cortex in humans is briefly described followed by some additional results concerning the location of the parietal eye field - within the posterior half of the intraparietal sulcus - and its role in visuo-spatial integration and attention. The other areas involved in spatial attention are also examined in the light of several recent contributing reports. Lastly, there are also new functional magnetic resonance imaging findings concerning the posterior cingulate cortex, which appears to be mainly involved in the control of externally guided eye movements and attentional mechanisms. Many new findings on the organization of saccades and pursuit eye movements at the cortical level have recently been reported. Furthermore, eye movements are increasingly used as a tool to elucidate relatively complex neuropsychological processes such as attention, spatial memory, motivation and decisional processes, and a considerable number of reports dealing with these questions have been observed. Show more