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

Department of Physiology, University of Wisconsin-Madison, School of Medicine and Public Health, Madison, Wisconsin 53706, USA.
The Journal of Neuroscience : The Official Journal of the Society for Neuroscience (Impact Factor: 6.34). 04/2008; 28(12):2991-3007. DOI: 10.1523/JNEUROSCI.5424-07.2008
Source: PubMed


How the brain selects one action from among multiple options is unknown. A main tenet of signal detection theory (SDT) is that sensory stimuli are represented as noisy information channels. Therefore, the accuracy of selection might be predicted by how well neuronal activity representing alternatives can be distinguished. Here, we apply an SDT framework to a motor system by recording from superior colliculus (SC) neurons during performance of a color, oddball selection task. We recorded from sets of four neurons simultaneously, each of the four representing one of the four possible targets. Because the electrode placement constrained the position of the stimuli in the visual field, the stimulus arrangement varied across experiments. This variability in stimulus arrangement led to variability in choices allowing us to explore the relationship between SC neuronal activity and performance accuracy. SC target neurons had higher levels of discharge than SC distractor neurons in subsets of trials when selection performance was very accurate. In subsets of trials when performance was poor, the discharge level decreased in target neurons and increased in distractor neurons. Accurate performance was associated with larger separations between neuronal activity from targets and distractors as quantified by the receiver operating characteristic (ROC) area and d' (an index of discriminability). Poorer performance was associated with less separation of target and distractor neuronal activity. ROC area and d' scaled approximately linearly with performance accuracy. Furthermore, ROC area and d' increased as saccade onset approached. Together, the results indicate that SC buildup neuronal activity signals the saccadic eye movement decision.

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Available from: Byounghoon Kim
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    • "Before that decision is made, however, preparatory oculomotor signals are generated for all available targets in the superior colliculus (Glimcher and Sparks, 1992; Basso and Wurtz, 1997), the lateral intraparietal area (LIP) (Platt and Glimcher, 1997; Shadlen and Newsome, 2001) and the frontal eye field (Schall and Hanes, 1993; Lee and Keller, 2008). The activity at multiple target locations is kept until close to the onset of the saccade (Thompson et al., 2005; Thomas and Pare, 2007; Kim and Basso, 2008). If feedback from these areas is the driving force behind peri-saccadic compression one might expect that compression will be generated to multiple foci. "
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    ABSTRACT: When visual stimuli are presented at the onset of a saccadic eye movement they are seen compressed onto the target location of the saccade. This peri-saccadic compression is believed to result from internal feedback pathways between oculomotor and visual areas of the brain. This feedback enhances vision around the saccade target at the expense of localization ability in other regions of the visual field. Although saccades can be targeted at only one object at a time, often multiple potential targets are available in a visual scene, and the oculomotor system has to choose which target to look at. If two targets are available, preparatory activity builds-up at both target locations in oculomotor maps. Here we show that, in this situation, two foci of compression develop, independent of which of the two targets is eventually chosen for the saccade. Our results suggest that theories that use oculomotor feedback as efference copy signals for upcoming eye movements should take the possibility into account that multiple feedback signals from potential targets may occur in parallel before the execution of a saccade.
    Full-text · Article · Oct 2015 · Frontiers in Systems Neuroscience
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    • "A large number of studies have utilized this process to study the way the brain makes decisions. By placing a choice target within the response field of a neuron within certain areas in the oculomotor system, we can observe how the responses change as a function of the final decision (Ding and Gold 2012; Horwitz et al. 2004; Kim and Basso 2008; Mirpour and Bisley 2012; Platt and Glimcher 1999; Shadlen and Newsome 2001). "
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    ABSTRACT: When looking around the world, we can only attend a limited number of locations. The lateral intraparietal area (LIP) is thought to play a role in guiding both covert attention and eye movements. In this study, we test the involvement of LIP in both mechanisms using a change detection task. In the task, animals had to indicate whether an element changed during a blank in the trial by making a saccade to it. If no element changed, they had to maintain fixation. We examine how the animals' behavior is biased based on LIP activity prior to the presentation of the stimulus the animal must respond to. When the activity was high, the animal was more likely to make an eye movement toward the stimulus, even if there was no change; when the activity was low, the animal either had a slower reaction time or maintained fixation, even if a change occurred. We conclude that LIP activity is involved in both covert and overt attention, but when decisions about eye movements are to be made, this role takes precedence over guiding covert attention. Copyright © 2015, Journal of Neurophysiology.
    Full-text · Article · Sep 2015 · Journal of Neurophysiology
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    • "All of the results described above were based entirely on modulation of discharge rates of individual neurons. It is clear, though, that saccade target selection is accomplished by pools of neurons [148] [174] [175] and probably entails more than just modulation of spike rate because cooperation and competition between pairs of neurons is modulated during target selection [176]. Indeed, correlation in discharge rates of FEF neurons over longer time scales has been reported even before stimulus presentation [177]. "
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    ABSTRACT: Primate vision is served by rapid shifts of gaze called saccades. This review will survey current knowledge and particular problems concerning the neural control and guidance of gaze shifts.
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