Visual Responses in FEF, Unlike V1, Primarily Reflect When the Visual Context Renders a Receptive Field Salient

A focus on the multiple interfaces between action and perception and their neural correlates

Successful behaviour relies on the appropriate interplay between action and perception. The well-established dorsal and ventral stream theories depicted two distinct functional pathways for the processes of action and perception, respectively. In physiological conditions, the two pathways closely cooperate in order to produce successful adaptive behaviour. As the coupling between perception and action exists, this requires an interface that is responsible for a common reading of the two functions. Several studies have proposed different types of perception and action interfaces, suggesting their role in the creation of the shared interaction channel. In the present review, we describe three possible perception and action interfaces: i) the motor code, including common coding approaches, ii) attention, and iii) object affordance; we highlight their potential neural correlates. From this overview, a recurrent neural substrate that underlies all these interface functions appears to be crucial: the parieto-frontal circuit. This network is involved in the mirror mechanism which underlies the perception and action interfaces identified as common coding and motor code theories. The same network is also involved in the spotlight of attention and in the encoding of potential action towards objects; these are manifested in the perception and action interfaces for common attention and object affordance, respectively. Within this framework, most studies were dedicated to the description of the role of the inferior parietal lobule; growing evidence, however, suggests that the superior parietal lobule also plays a crucial role in the interplay between action and perception. The present review proposes a novel model that is inclusive of the superior parietal regions and their relative contribution to the different action and perception interfaces.

Using Natural Scenes to Enhance our Understanding of the Cerebral Cortex's Role in Visual Search

Using natural scenes is an approach to studying the visual and eye movement systems approximating how these systems function in everyday life. This review examines the results from behavioral and neurophysiological studies using natural scene viewing in humans and monkeys. The use of natural scenes for the study of cerebral cortical activity is relatively new and presents challenges for data analysis. Methods and results from the use of natural scenes for the study of the visual and eye movement cortex are presented, with emphasis on new insights that this method provides enhancing what is known about these cortical regions from the use of conventional methods.

Stimulus salience conflicts and colludes with endogenous goals during urgent choices

Selecting where to look next depends on both the salience of objects and current goals (what we are looking for), but discerning their relative contributions over the time frame of typical visuomotor decisions (200-250 ms) has been difficult. Here we investigate this problem using an urgent choice task with which the two contributions can be dissociated and tracked moment by moment. Behavioral data from three monkeys corresponded with model-based predictions: when salience favored the target, perceptual performance evolved rapidly and steadily toward an asymptotic level; when salience favored the distracter, many rapid errors were produced and the rise in performance took more time-effects analogous to oculomotor and attentional capture. The results show that salience has a brief (∼50 ms) but inexorable impact that leads to exogenous, involuntary capture, and this can either help or hinder performance, depending on the alignment between salience and ongoing internal goals.

Neuronal congruency effects in macaque prefrontal cortex

The interplay between task-relevant and task-irrelevant information may induce conflicts that impair behavioral performance, a.k.a. behavioral congruency effects. The neuronal mechanisms underlying behavioral congruency effects, however, are poorly understood. We recorded single unit activity in monkey prefrontal cortex using a task-switching paradigm and discovered a neuronal congruency effect (NCE) that is carried by target and distractor neurons which process target and distractor-related information, respectively. The former neurons provide more signal, the latter less noise in congruent compared to incongruent conditions, resulting in a better target representation. Such NCE is dominated by the level of congruency, and is not determined by the task rules the subjects used, their reaction times (RT), the length of the delay period, nor the response levels of the neurons. We propose that this NCE can explain behavioral congruency effects in general, as well as previous fMRI and EEG results in various conflict paradigms.

Stimulus-induced conflicts impair behavior in conflict tasks resulting in a phenomenon known as the behavioral congruency effect. Here, the authors investigate the neural underpinnings of this phenomenon and report a neuronal congruency effect in macaque prefrontal cortex to explain this impairment.

Under time pressure, the exogenous modulation of saccade plans is ubiquitous, intricate, and lawful

The choice of where to look next is determined by both exogenous (bottom-up) and endogenous (top-down) factors, but details of their interaction and distinct contributions to target selection have remained elusive. Recent experiments with urgent choice tasks, in which stimuli are evaluated while motor plans are already advancing, have greatly clarified these contributions. Specifically, exogenous modulations associated with stimulus detection act rapidly and briefly (∼25 ms) to automatically halt and/or boost ongoing motor plans as per spatial congruence rules. These stereotypical modulations explain, in quantitative detail, characteristic features of many saccadic tasks (e.g. antisaccade, countermanding, saccadic-inhibition, gap, and double-step). Thus, the same low-level visuomotor interactions contribute to diverse oculomotor phenomena traditionally attributed to different neural mechanisms.

Urgent Decision Making: Resolving Visuomotor Interactions at High Temporal Resolution

Measuring when exactly perceptual decisions are made is crucial for defining how the activation of specific neurons contributes to behavior. However, in traditional, nonurgent visuomotor tasks, the uncertainty of this temporal measurement is very large. This is a problem not only for delimiting the capacity of perception, but also for correctly interpreting the functional roles ascribed to choice-related neuronal responses. In this article, we review psychophysical, neurophysiological, and modeling work based on urgent visuomotor tasks in which this temporal uncertainty can be effectively overcome. The cornerstone of this work is a novel behavioral metric that describes the evolution of the subject's perceptual judgment moment by moment, allowing us to resolve numerous perceptual events that unfold within a few tens of milliseconds. In this framework, the neural distinction between perceptual evaluation and motor selection processes becomes particularly clear, as the conclusion of one is not contingent on that of the other. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Neurochemistry of Visual Attention

Visual attention is the cognitive process that mediates the selection of important information from the environment. This selection is usually controlled by bottom-up and top-down attentional biasing. Since for most humans vision is the dominant sense, visual attention is critically important for higher-order cognitive functions and related deficits are a core symptom of many neuropsychiatric and neurological disorders. Here, we summarize the importance and relative contributions of different neuromodulators and neurotransmitters to the neural mechanisms of top-down and bottom-up attentional control. We will not only review the roles of widely accepted neuromodulators, such as acetylcholine, dopamine and noradrenaline, but also the contributions of other modulatory substances. In doing so, we hope to shed some light on the current understanding of the role of neurochemistry in shaping neuron properties contributing to the allocation of attention in the visual field.

Top-down control of saccades requires inhibition of suddenly appearing stimuli

Humans scan their visual environment using saccade eye movements. Where we look is influenced by bottom-up salience and top-down factors, like value. For reactive saccades in response to suddenly appearing stimuli, it has been shown that short-latency saccades are biased towards salience, and that top-down control increases with increasing latency. Here, we show, in a series of six experiments, that this transition towards top-down control is not determined by the time it takes to integrate value information into the saccade plan, but by the time it takes to inhibit suddenly appearing salient stimuli. Participants made consecutive saccades to three fixation crosses and a vertical bar consisting of a high-salient and a rewarded low-salient region. Endpoints on the bar were biased towards salience whenever it appeared or reappeared shortly before the last saccade was initiated. This was also true when the eye movement was already planned. When the location of the suddenly appearing salient region was predictable, saccades were aimed in the opposite direction to nullify this sudden onset effect. Successfully inhibiting salience, however, could only be achieved by previewing the target. These findings highlight the importance of inhibition for top-down eye-movement control.

Spatial attention enhances network, cellular and subthreshold responses in mouse visual cortex

Internal brain states strongly modulate sensory processing during behaviour. Studies of visual processing in primates show that attention to space selectively improves behavioural and neural responses to stimuli at the attended locations. Here we develop a visual spatial task for mice that elicits behavioural improvements consistent with the effects of spatial attention, and simultaneously measure network, cellular, and subthreshold activity in primary visual cortex. During trial-by-trial behavioural improvements, local field potential (LFP) responses to stimuli detected inside the receptive field (RF) strengthen. Moreover, detection inside the RF selectively enhances excitatory and inhibitory neuron responses to task-irrelevant stimuli and suppresses noise correlations and low frequency LFP fluctuations. Whole-cell patch-clamp recordings reveal that detection inside the RF increases synaptic activity that depolarizes membrane potential responses at the behaviorally relevant location. Our study establishes that mice display fundamental signatures of visual spatial attention spanning behavioral, network, cellular, and synaptic levels, providing new insight into rapid cognitive enhancement of sensory signals in visual cortex.

Extensive research in primates shows that attention to space improves behavioural performance as well as neural responses to stimuli in that location. Here, the authors establish a visual spatial attention task in mice and report on attentional modulation of behaviour, as well as neural correlates from subthreshold responses in single cells to spikes and LFP at network level.

Timing Determines Tuning: A Rapid Spatial Transformation in Superior Colliculus Neurons during Reactive Gaze Shifts

Gaze saccades, rapid shifts of the eyes and head toward a goal, have provided fundamental insights into the neural control of movement. For example, it has been shown that the superior colliculus (SC) transforms a visual target (T) code to future gaze (G) location commands after a memory delay. However, this transformation has not been observed in "reactive" saccades made directly to a stimulus, so its contribution to normal gaze behavior is unclear. Here, we tested this using a quantitative measure of the intermediate codes between T and G, based on variable errors in gaze endpoints. We demonstrate that a rapid spatial transformation occurs within the primate's SC (Macaca mulatta) during reactive saccades, involving a shift in coding from T, through intermediate codes, to G. This spatial shift progressed continuously both across and within cell populations [visual, visuomotor (VM), motor], rather than relaying discretely between populations with fixed spatial codes. These results suggest that the SC produces a rapid, noisy, and distributed transformation that contributes to variable errors in reactive gaze shifts.

Voluntary and involuntary contributions to perceptually guided saccadic choices resolved with millisecond precision

In the antisaccade task, which is considered a sensitive assay of cognitive function, a salient visual cue appears and the participant must look away from it. This requires sensory, motor-planning, and cognitive neural mechanisms, but what are their unique contributions to performance, and when exactly are they engaged? Here, by manipulating task urgency, we generate a psychophysical curve that tracks the evolution of the saccadic choice process with millisecond precision, and resolve the distinct contributions of reflexive (exogenous) and voluntary (endogenous) perceptual mechanisms to antisaccade performance over time. Both progress extremely rapidly, the former driving the eyes toward the cue early on (∼100 ms after cue onset) and the latter directing them away from the cue ∼40 ms later. The behavioral and modeling results provide a detailed, dynamical characterization of attentional and oculomotor capture that is not only qualitatively consistent across participants, but also indicative of their individual perceptual capacities.

All-or-None Context Dependence Delineates Limits of FEF Visual Target Selection

Choices of where to look are informed by perceptual judgments, which locate objects of current value or interest within the visual scene. This perceptual-motor transform is partly implemented in the frontal eye field (FEF), where visually responsive neurons appear to select behaviorally relevant visual targets and, subsequently, saccade-related neurons select the movements required to look at them. Here, we use urgent decision-making tasks to show (1) that FEF motor activity can direct accurate, visually informed choices in the complete absence of prior target-distracter discrimination by FEF visual responses and (2) that such discrimination by FEF visual cells shows an all-or-none reliance on the presence of stimulus attributes strongly associated with saliency-driven attentional allocation. The present findings suggest that FEF visual target selection is specific to visual judgments made on the basis of saliency and may not play a significant role in guiding saccadic choices informed solely by feature content.

More than Just a "Motor": Recent Surprises from the Frontal Cortex

Motor and premotor cortices are crucial for the control of movements. However, we still know little about how these areas contribute to higher-order motor control, such as deciding which movements to make and when to make them. Here we focus on rodent studies and review recent findings, which suggest that-in addition to motor control-neurons in motor cortices play a role in sensory integration, behavioral strategizing, working memory, and decision-making. We suggest that these seemingly disparate functions may subserve an evolutionarily conserved role in sensorimotor cognition and that further study of rodent motor cortices could make a major contribution to our understanding of the evolution and function of the mammalian frontal cortex.

Saccadic inhibition interrupts ongoing oculomotor activity to enable the rapid deployment of alternate movement plans

Diverse psychophysical and neurophysiological results show that oculomotor networks are continuously active, such that plans for making the next eye movement are always ongoing. So, when new visual information arrives unexpectedly, how are those plans affected? At what point can the new information start guiding an eye movement, and how? Here, based on modeling and simulation results, we make two observations that are relevant to these questions. First, we note that many experiments, including those investigating the phenomenon known as "saccadic inhibition", are consistent with the idea that sudden-onset stimuli briefly interrupt the gradual rise in neural activity associated with the preparation of an impending saccade. And second, we show that this stimulus-driven interruption is functionally adaptive, but only if perception is fast. In that case, putting on hold an ongoing saccade plan toward location A allows the oculomotor system to initiate a concurrent, alternative plan toward location B (where a stimulus just appeared), deliberate (briefly) on the priority of each target, and determine which plan should continue. Based on physiological data, we estimate that the advantage of this strategy, relative to one in which any plan once initiated must be completed, is of several tens of milliseconds per saccade.

Neural Circuits That Mediate Selective Attention: A Comparative Perspective

Selective attention is central to cognition. Dramatic advances have been made in understanding the neural circuits that mediate selective attention. Forebrain networks, most elaborated in primates, control all forms of attention based on task demands and the physical salience of stimuli. These networks contain circuits that distribute top-down signals to sensory processing areas and enhance information processing in those areas. A midbrain network, most elaborated in birds, controls spatial attention. It contains circuits that continuously compute the highest priority stimulus location and route sensory information from the selected location to forebrain networks that make cognitive decisions. The identification of these circuits, their functions and mechanisms represent a major advance in our understanding of how the vertebrate brain mediates selective attention.