Neural Correlates of warning Warning signals influence motor processing

5 Figures 28 Pages (including references and figure captions) Summary When observers initiate responses to visual targets, they do so sooner when a preceding stimulus indicates that the target will appear shortly. This consequence of a warning signal may change neural activity in one of four ways. On the sensory side, the warning signal may speed up the rate at which the target is registered by the brain or enhance the magnitude of its signal. On the motor end, the warning signal may lower the threshold required to initiate a response or speed up the rate at which activity accumulates to reach threshold. Here, we describe which explanation is better supported. To accomplish this end, monkeys performed different versions of a cue-target task, while we monitored the activity of visuomotor and motor neurons in the superior colliculus. Although the cue target task was designed to measure the properties of reflexive spatial attention, there are two events in this task that produce non-specific warning effects: a central reorienting event (brightening of central fixation marker) that is used to direct attention away from the cue, and the presentation of the cue itself. Monopolizing upon these tendencies, we show that warning effects are associated with several changes in neural activity: the target-related response is enhanced, the threshold for initiating a saccade is lowered, and the rate at which activity accumulates towards threshold rises faster. Ultimately, the accumulation of activity towards threshold predicted behavior most closely. In the discussion, we describe the implications and limitations of these data for theories of warning effects and potential avenues for future research. 3 of 31 The study of warning effects is one of the oldest topics in the field of Psychology. Wundt (1881) observed that participants initiate responses sooner when a stimulus (the warning signal) indicates that the target will appear shortly (cited in Hackley & Valle-Inclán, 2003; James, 1890; Fig. 1A). Since this time, many different ideas have circulated regarding how warning signals exert their effect. Some researchers have proposed that warning signals influence sensory or perceptual processing, whereas others have proposed that warning signals influence response selection or the execution of action. In this study, our goal was to translate these different models into direct predictions that could be tested in single neuron neurophysiology (Fig. 1B). The sensory/perceptual accounts propose that a warning signal modifies how the target is processed in the brain. There are …