Collicular involvement in a saccadic colour discrimination task

Abstract

We have recorded the neural activity of single superior colliculus (SC) neurons in monkeys engaged in a saccadic target/nontarget discrimination task based on a colour cue. Since correct execution of this task probably depends on cortical signal processing, our experiments are of interest for getting a better insight in the problem of how cortical and subcortical signals, relevant for the visual guidance of saccades, are combined. The experiments were designed to distinguish between two extreme possibilities: The crucial cortical signal affects the saccadic system at or above the level of the SC movement-related cells (serial hypothesis); The colour-based target information bypasses the motor colliculus and affects the saccadic system at a level more downstream (bypass hypothesis). Under conditions where the saccadic system had to select a green target stimulus and to ignore the red nontarget spot, the saccade-related activity in SC visuomotor neurons remained as tightly coupled to the metrics of the saccade as it was in a simple spot-detection task. Since the saccade-related activity of these cells appeared to be based on colour information, we conclude that our data corroborate the serial hypothesis. The initial activity after stimulus onset appeared to be colour nonopponent in all neurons. In some cells the neural activity was quantitatively slightly different for the green target and the red nontarget. Since these minor differences were colour rather than motor response dependent, they were probably not part of the target-selection process. These data suggest the possibility that the decision as to which saccade should be made was largely imposed upon the SC visuomotor cells by an external source. We discuss various possibilities for the origin of the putative intervening signal which orders a saccade by causing a burst in the appropriate SC visuomotor neurons.

A competitive integration model of exogenous and endogenous eye movements

“…This seems to imply that distractor-evoked inhibition is sensitive to the location of the distractor. Physiological and anatomical evidence (Johnson and Everling 2006;Krauzlis et al 2004;McPeek and Keller 2002a;Ottes et al 1987) is consistent with both location-specific and broad inhibition. For example, Johnson et al (2006) found that, during an antisaccade task, DLPFC neurons sent input that was assumed to be inhibitory to the colliculus in which prosaccades were programmed.…”

Saccade Target Selection in the Superior Colliculus: A Signal Detection Theory Approach

“…Traditionally, experiments in SC were performed with single spots of light as targets for saccades. More recently, recordings of SC neurons occur in the presence of more complex stimulus displays that include targets and distractors (Ottes et al, 1987;Glimcher and Sparks, 1993;Basso and Wurtz, 1998;Edelman and Keller, 1998;McPeek and Keller, 2002;Port and Wurtz, 2003). The stimulus displays are sometimes adopted from those used in psychophysical experiments designed to explore visual search (Treisman and Gelade, 1980;Egeth and Yantis, 1997;Schall and Thompson, 1999;Palmer et al, 2000;Wolfe and Horowitz, 2004).…”

The effect of stimuli that isolate S-cones on early saccades and the gap effect

“…As the magnocellular pathway is not colour opponent and so does not carry colour information, this renders the SC insensitive to colour (Marrocco & Li 1977). Although colour-opponent saccade-related activity can develop within the SC under appropriate circumstances, the initial sensory response of neurons is non-opponent (Ottes et al 1987). Therefore, it should be possible to abolish all direct visual input to the SC-whether it be from the retina or from the cortex-by using appropriately selected coloured targets.…”