A mechanism for decision rule discrimination by supplementary eye field neurons

Influence of the Location of a Decision Cue on the Dynamics of Pupillary Light Response

The pupils of the eyes reflexively constrict in light and dilate in dark to optimize retinal illumination. Non-visual cognitive factors, like attention, arousal, decision-making, etc., also influence pupillary light response (PLR). During passive viewing, the eccentricity of a stimulus modulates the pupillary aperture size driven by spatially weighted corneal flux density (CFD), which is the product of luminance and the area of the stimulus. Whether the scope of attention also influences PLR remains unclear. In this study, we contrasted the pupil dynamics between diffused and focused attentional conditions during decision-making, while the global CFD remained the same in the two conditions. A population of 20 healthy humans participated in a pair of forced choice tasks. They distributed attention to the peripheral decision cue in one task, and concentrated at the center in the other to select the target from four alternatives for gaze orientation. The location of this cue did not influence participants' reaction time (RT). However, the magnitude of constriction was significantly less in the task that warranted attention to be deployed at the center than on the periphery. We observed similar pupil dynamics when participants either elicited or canceled a saccadic eye movement, which ruled out pre-saccadic obligatory attentional orientation contributing to PLR. We further addressed how the location of attentional deployment might have influenced PLR. We simulated a biomechanical model of PLR with visual stimulation of different strengths as inputs corresponding to the two attentional conditions. In this homeomorphic model, the computational characteristic of each element was derived from the physiological and/or mechanical properties of the corresponding biological element. The simulation of this model successfully mimicked the observed data. In contrast to common belief that the global ambient luminosity drives pupillary response, the results of our study suggest that the effective CFD (eCFD) determined via the luminance multiplied by the size of the stimulus at the location of deployed attention in the visual space is critical for the magnitude of pupillary constriction.

Flexible Sensorimotor Computations through Rapid Reconfiguration of Cortical Dynamics

Neural mechanisms that support flexible sensorimotor computations are not well understood. In a dynamical system whose state is determined by interactions among neurons, computations can be rapidly reconfigured by controlling the system's inputs and initial conditions. To investigate whether the brain employs such control mechanisms, we recorded from the dorsomedial frontal cortex of monkeys trained to measure and produce time intervals in two sensorimotor contexts. The geometry of neural trajectories during the production epoch was consistent with a mechanism wherein the measured interval and sensorimotor context exerted control over cortical dynamics by adjusting the system's initial condition and input, respectively. These adjustments, in turn, set the speed at which activity evolved in the production epoch, allowing the animal to flexibly produce different time intervals. These results provide evidence that the language of dynamical systems can be used to parsimoniously link brain activity to sensorimotor computations.

Superior colliculus signals decisions rather than confidence: analysis of single neurons

Recent findings indicate that monkeys can report their confidence in perceptual decisions and that this information is encoded in neurons involved in making decisions, including the lateral intraparietal area (LIP) and the supplementary eye field (SEF). A key issue to consider when studying confidence is that decision accuracy often correlates with confidence reports; when we are performing well, we generally feel more confident. Expanding on work performed in humans, we designed a novel task for monkeys that dissociates perceptual information leading to decisions from perceptual information leading to confidence reports. Using this task, we recently showed that decoded ensemble activity recorded from the superior colliculus (SC) reflected decisions rather than confidence reports. However, our previous population level analysis collapsed over multiple SC neuronal types and therefore left open the possibility that first, individual discharge rates might encode information related to decision confidence, and second, different neuronal cell types within the SC might signal decision confidence independently of decision accuracy. We found that when decision accuracy and decision confidence covaried, modulation occurred primarily in neurons with prelude activity (buildup neurons). However, isolating decision confidence from decision accuracy uncovered that only a few, primarily buildup neurons showed signals correlating uniquely with decision confidence and the effect sizes were very small. Based on this work and our previous work using decoding methods, we conclude that neuronal signals for decision confidence, independent of decision accuracy, are unlikely to exist at the level of single or populations of neurons in the SC. Our results together with other recent work call into question normative models of confidence based on the optimal readout of decision signals. NEW & NOTEWORTHY Models of decision confidence suggest that our sense of confidence is an optimal readout of perceptual decision signals. Here, we report that a subcortical area, the superior colliculus (SC), contains neurons with activity that signal decisions and confidence in a task in which decision accuracy and confidence covary, similar to area lateral intraparietal area in cortex. The signals from SC occur primarily in the neurons with prelude activity (buildup neurons). However, in a task that dissociates decision accuracy from decision confidence, we find that only a few individual neurons express unique signals of confidence. These results call into question normative models of confidence based on optimal readout of perceptual decision signals.