Intelligent behaviour requires self-control based on the consequences of actions. The countermand... more Intelligent behaviour requires self-control based on the consequences of actions. The countermanding task is designed to study self-control; it requires subjects to withhold planned movements in response to an imperative stop signal, which they can do with varying success. In humans, the medial frontal cortex has been implicated in the supervisory control of action. In monkeys, the supplementary eye field
When observers initiate responses to visual targets, they do so sooner when a preceding stimulus ... more 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 nonspecific 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 on 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 toward threshold rises faster. Ultimately, the accumulation of activity toward 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.
Consensus is emerging that the medial frontal lobe of the brain is involved in monitoring perform... more Consensus is emerging that the medial frontal lobe of the brain is involved in monitoring performance, but precisely what is monitored remains unclear. A saccade-countermanding task affords an experimental dissociation of neural signals of error, reinforcement, and conflict. Single-unit activity was monitored in the anterior cingulate cortex of monkeys performing this task. Neurons that signaled errors were found, half of which responded to the omission of earned reinforcement. A further diversity of neurons signaled earned or unexpected reinforcement. No neurons signaled the form of conflict engendered by interruption of saccade preparation produced in this task. These results are consistent with the hypothesis that the anterior cingulate cortex monitors the consequences of actions.
New Approaches for Studying Sensorimotor Integration, 2003
... viscoelastic forces and keep the eyes at an eccentric location in the orbit. These tonic ...m... more ... viscoelastic forces and keep the eyes at an eccentric location in the orbit. These tonic ...microsaccades 57 , smooth pursuit 58,59 , and vergence eye movements 60 . ... for saccades 79-81 . FEF is also known to play a direct role in producing saccadic eye movements. Low ...
Cognitive control impairments are linked to functional outcome in schizophrenia. The goal of the ... more Cognitive control impairments are linked to functional outcome in schizophrenia. The goal of the current study was to investigate precise abnormalities in two aspects of cognitive control: reactively changing a prepared response, and monitoring performance and adjusting behavior accordingly. We adapted an oculomotor task from neurophysiological studies of the cellular basis of cognitive control in nonhuman primates. 16 medicated outpatients with schizophrenia (SZ) and 18 demographically-matched healthy controls performed the modified double-step task. In this task, participants were required to make a saccade to a visual target. Infrequently, the target jumped to a new location and participants were instructed to rapidly inhibit and change their response. A race model provided an estimate of the time needed to cancel a planned movement. Response monitoring was assessed by measuring reaction time (RT) adjustments based on trial history. SZ patients had normal visually-guided saccadic...
The interactive race model of saccadic countermanding assumes that response inhibition results fr... more The interactive race model of saccadic countermanding assumes that response inhibition results from an interaction between a go unit, identified with gaze-shifting neurons, and a stop unit, identified with gaze-holding neurons, in which activation of the stop unit inhibits the growth of activation in the go unit to prevent it from reaching threshold. The interactive race model accounts for behavioral data and predicts physiological data in monkeys performing the stop-signal task. We propose an alternative model that assumes that response inhibition results from blocking the input to the go unit. We show that the blocked-input model accounts for behavioral data as accurately as the original interactive race model and predicts aspects of the physiological data more accurately. We extend the models to address the steady-state fixation period before the go stimulus is presented and find that the blocked-input model fits better than the interactive race model. We consider a model in whic...
The primate cortico-basal ganglia circuits are understood to be segregated into parallel anatomic... more The primate cortico-basal ganglia circuits are understood to be segregated into parallel anatomically and functionally distinct loops. Anatomical and physiological studies in macaque monkeys are summarized as showing that an oculomotor loop begins with projections from the frontal eye fields (FEF) to the caudate nucleus, and a motor loop begins with projections from the primary motor cortex (M1) to the putamen. However, recent functional and structural neuroimaging studies of the human cortico-striatal system report evidence inconsistent with this organization. To obtain conclusive evidence, we directly compared the pattern of connectivity between cortical motor areas and the striatum in humans and macaques in vivo using probabilistic diffusion tractography. In macaques we found that FEF is connected with the head of the caudate and anterior putamen, and M1 is connected with more posterior sections of caudate and putamen, corroborating neuroanatomical tract tracing findings. However...
The supplementary eye field registers the occurrence of conflict, errors and reward in macaque mo... more The supplementary eye field registers the occurrence of conflict, errors and reward in macaque monkeys performing a saccade-countermanding task. Using intracortical microstimulation, we determined whether the supplementary eye field only monitors or can actually influence performance. Weak microstimulation of many sites in the supplementary eye field improved monkeys' performance on a 'stop signal' task by delaying saccade initiation. This effect depended on the context of the task because simple visually guided saccades were not delayed by the same stimulation. These results demonstrate that the supplementary eye field can exert contextual executive control over saccade generation.
To investigate how the brain combines knowledge with visual processing to locate eye movement tar... more To investigate how the brain combines knowledge with visual processing to locate eye movement targets, we trained monkeys to search for a target defined by a conjunction of color and shape. On successful trials, neurons in the frontal eye field not only discriminated the target from distractors, but also discriminated distractors that shared a target feature as well as distractors that had been the search target during the previous session. Likewise, occasional errant saccades tended to direct gaze to distractors that either resembled the current target or had been the previous target. These findings show that the frontal eye field is involved in visual and not just motor selection and that visual selection is influenced by long-term priming. The data support the hypothesis that visual selection can be accomplished by parallel processing of objects based on their elementary features.
Intelligent behaviour requires self-control based on the consequences of actions. The countermand... more Intelligent behaviour requires self-control based on the consequences of actions. The countermanding task is designed to study self-control; it requires subjects to withhold planned movements in response to an imperative stop signal, which they can do with varying success. In humans, the medial frontal cortex has been implicated in the supervisory control of action. In monkeys, the supplementary eye field in the dorsomedial frontal cortex is involved in producing eye movements, but its precise function has not been clarified. To investigate the role of the supplementary eye field in the control of eye movements, we recorded neural activity in macaque monkeys trained to perform an eye movement countermanding task. Distinct groups of neurons were active after errors, after successful withholding of a partially prepared movement, or in association with reinforcement. These three forms of activation could not be explained by sensory or motor factors. Our results lead us to put forward t...
Previous research has shown that visually responsive neurons in the frontal eye field of macaque ... more Previous research has shown that visually responsive neurons in the frontal eye field of macaque monkeys select the target for a saccade during efficient, pop-out visual search through suppression of the representation of the nontarget distractors. For a fraction of these neurons, the magnitude of this distractor suppression varied with the proximity of the target to the receptive field, exhibiting more suppression of the distractor representation when the target was nearby than when the target was distant. The purpose of this study was to determine whether the variation of distractor suppression related to target proximity varied with target-distractor feature similarity. The effect of target proximity on distractor suppression did not vary with target-distractor similarity and therefore may be an endogenous property of the selection process.
The objective of the present study was to compare two components of executive functioning, respon... more The objective of the present study was to compare two components of executive functioning, response monitoring and inhibition, in bipolar disorder (BP) and schizophrenia (SZ). The saccadic countermanding task is a translational paradigm optimized for detecting subtle abnormalities in response monitoring and response inhibition. We have previously reported countermanding performance abnormalities in SZ, but the degree to which these impairments are shared by other psychotic disorders is unknown. 18 BP, 17 SZ, and 16 demographically matched healthy controls (HC) participated in a saccadic countermanding task. Performance on the countermanding task is approximated as a race between movement generation and inhibition processes; this model provides an estimate of the time needed to cancel a planned movement. Response monitoring was assessed by the reaction time (RT) adjustments based on trial history. Like SZ patients, BP patients needed more time to cancel a planned movement. The two pa...
Endorsing the conceptual clarity of Nachev and Hacker, we offer an alternative perspective on int... more Endorsing the conceptual clarity of Nachev and Hacker, we offer an alternative perspective on intention and action that focuses on consequences instead of the antecedents of action. We propose that given many-to-one mapping of brain states to body movements, the brain processes that monitor action consequences offer a reconciliation of intentional reasons with neural causes. This proposal offers an enriched compatibilist position providing useful leverage on questions of responsibility and culpability.
The neural link between a sensory signal and its behavioral report was investigated in macaques t... more The neural link between a sensory signal and its behavioral report was investigated in macaques trained to locate an intermittently detectable visual target. Neurons in the frontal eye field, an area involved in converting the outcome of visual processing into motor ...
To determine whether visual discrimination in macaque frontal eye field (FEF) is contingent on sa... more To determine whether visual discrimination in macaque frontal eye field (FEF) is contingent on saccade planning, unit activity was recorded in two monkeys during blocked go and no-go visual search trials. The eye movements made by monkeys after correct no-go trials, in addition to an attenuation of the visual responses in no-go trials compared with go trials, indicated that covert saccade planning was effectively discouraged. During no-go search trials, the activity of the majority of neurons evolved to signal the location of the oddball stimulus. The degree and time course of the stimulus discrimination process observed in no-go trials was not different from that observed in go trials. We conclude that the discrimination of a salient visual stimulus reflected by FEF neurons is not contingent on saccade production but rather may reflect the outcome of an automatic visual selection process.
Intelligent behaviour requires self-control based on the consequences of actions. The countermand... more Intelligent behaviour requires self-control based on the consequences of actions. The countermanding task is designed to study self-control; it requires subjects to withhold planned movements in response to an imperative stop signal, which they can do with varying success. In humans, the medial frontal cortex has been implicated in the supervisory control of action. In monkeys, the supplementary eye field
When observers initiate responses to visual targets, they do so sooner when a preceding stimulus ... more 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 nonspecific 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 on 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 toward threshold rises faster. Ultimately, the accumulation of activity toward 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.
Consensus is emerging that the medial frontal lobe of the brain is involved in monitoring perform... more Consensus is emerging that the medial frontal lobe of the brain is involved in monitoring performance, but precisely what is monitored remains unclear. A saccade-countermanding task affords an experimental dissociation of neural signals of error, reinforcement, and conflict. Single-unit activity was monitored in the anterior cingulate cortex of monkeys performing this task. Neurons that signaled errors were found, half of which responded to the omission of earned reinforcement. A further diversity of neurons signaled earned or unexpected reinforcement. No neurons signaled the form of conflict engendered by interruption of saccade preparation produced in this task. These results are consistent with the hypothesis that the anterior cingulate cortex monitors the consequences of actions.
New Approaches for Studying Sensorimotor Integration, 2003
... viscoelastic forces and keep the eyes at an eccentric location in the orbit. These tonic ...m... more ... viscoelastic forces and keep the eyes at an eccentric location in the orbit. These tonic ...microsaccades 57 , smooth pursuit 58,59 , and vergence eye movements 60 . ... for saccades 79-81 . FEF is also known to play a direct role in producing saccadic eye movements. Low ...
Cognitive control impairments are linked to functional outcome in schizophrenia. The goal of the ... more Cognitive control impairments are linked to functional outcome in schizophrenia. The goal of the current study was to investigate precise abnormalities in two aspects of cognitive control: reactively changing a prepared response, and monitoring performance and adjusting behavior accordingly. We adapted an oculomotor task from neurophysiological studies of the cellular basis of cognitive control in nonhuman primates. 16 medicated outpatients with schizophrenia (SZ) and 18 demographically-matched healthy controls performed the modified double-step task. In this task, participants were required to make a saccade to a visual target. Infrequently, the target jumped to a new location and participants were instructed to rapidly inhibit and change their response. A race model provided an estimate of the time needed to cancel a planned movement. Response monitoring was assessed by measuring reaction time (RT) adjustments based on trial history. SZ patients had normal visually-guided saccadic...
The interactive race model of saccadic countermanding assumes that response inhibition results fr... more The interactive race model of saccadic countermanding assumes that response inhibition results from an interaction between a go unit, identified with gaze-shifting neurons, and a stop unit, identified with gaze-holding neurons, in which activation of the stop unit inhibits the growth of activation in the go unit to prevent it from reaching threshold. The interactive race model accounts for behavioral data and predicts physiological data in monkeys performing the stop-signal task. We propose an alternative model that assumes that response inhibition results from blocking the input to the go unit. We show that the blocked-input model accounts for behavioral data as accurately as the original interactive race model and predicts aspects of the physiological data more accurately. We extend the models to address the steady-state fixation period before the go stimulus is presented and find that the blocked-input model fits better than the interactive race model. We consider a model in whic...
The primate cortico-basal ganglia circuits are understood to be segregated into parallel anatomic... more The primate cortico-basal ganglia circuits are understood to be segregated into parallel anatomically and functionally distinct loops. Anatomical and physiological studies in macaque monkeys are summarized as showing that an oculomotor loop begins with projections from the frontal eye fields (FEF) to the caudate nucleus, and a motor loop begins with projections from the primary motor cortex (M1) to the putamen. However, recent functional and structural neuroimaging studies of the human cortico-striatal system report evidence inconsistent with this organization. To obtain conclusive evidence, we directly compared the pattern of connectivity between cortical motor areas and the striatum in humans and macaques in vivo using probabilistic diffusion tractography. In macaques we found that FEF is connected with the head of the caudate and anterior putamen, and M1 is connected with more posterior sections of caudate and putamen, corroborating neuroanatomical tract tracing findings. However...
The supplementary eye field registers the occurrence of conflict, errors and reward in macaque mo... more The supplementary eye field registers the occurrence of conflict, errors and reward in macaque monkeys performing a saccade-countermanding task. Using intracortical microstimulation, we determined whether the supplementary eye field only monitors or can actually influence performance. Weak microstimulation of many sites in the supplementary eye field improved monkeys' performance on a 'stop signal' task by delaying saccade initiation. This effect depended on the context of the task because simple visually guided saccades were not delayed by the same stimulation. These results demonstrate that the supplementary eye field can exert contextual executive control over saccade generation.
To investigate how the brain combines knowledge with visual processing to locate eye movement tar... more To investigate how the brain combines knowledge with visual processing to locate eye movement targets, we trained monkeys to search for a target defined by a conjunction of color and shape. On successful trials, neurons in the frontal eye field not only discriminated the target from distractors, but also discriminated distractors that shared a target feature as well as distractors that had been the search target during the previous session. Likewise, occasional errant saccades tended to direct gaze to distractors that either resembled the current target or had been the previous target. These findings show that the frontal eye field is involved in visual and not just motor selection and that visual selection is influenced by long-term priming. The data support the hypothesis that visual selection can be accomplished by parallel processing of objects based on their elementary features.
Intelligent behaviour requires self-control based on the consequences of actions. The countermand... more Intelligent behaviour requires self-control based on the consequences of actions. The countermanding task is designed to study self-control; it requires subjects to withhold planned movements in response to an imperative stop signal, which they can do with varying success. In humans, the medial frontal cortex has been implicated in the supervisory control of action. In monkeys, the supplementary eye field in the dorsomedial frontal cortex is involved in producing eye movements, but its precise function has not been clarified. To investigate the role of the supplementary eye field in the control of eye movements, we recorded neural activity in macaque monkeys trained to perform an eye movement countermanding task. Distinct groups of neurons were active after errors, after successful withholding of a partially prepared movement, or in association with reinforcement. These three forms of activation could not be explained by sensory or motor factors. Our results lead us to put forward t...
Previous research has shown that visually responsive neurons in the frontal eye field of macaque ... more Previous research has shown that visually responsive neurons in the frontal eye field of macaque monkeys select the target for a saccade during efficient, pop-out visual search through suppression of the representation of the nontarget distractors. For a fraction of these neurons, the magnitude of this distractor suppression varied with the proximity of the target to the receptive field, exhibiting more suppression of the distractor representation when the target was nearby than when the target was distant. The purpose of this study was to determine whether the variation of distractor suppression related to target proximity varied with target-distractor feature similarity. The effect of target proximity on distractor suppression did not vary with target-distractor similarity and therefore may be an endogenous property of the selection process.
The objective of the present study was to compare two components of executive functioning, respon... more The objective of the present study was to compare two components of executive functioning, response monitoring and inhibition, in bipolar disorder (BP) and schizophrenia (SZ). The saccadic countermanding task is a translational paradigm optimized for detecting subtle abnormalities in response monitoring and response inhibition. We have previously reported countermanding performance abnormalities in SZ, but the degree to which these impairments are shared by other psychotic disorders is unknown. 18 BP, 17 SZ, and 16 demographically matched healthy controls (HC) participated in a saccadic countermanding task. Performance on the countermanding task is approximated as a race between movement generation and inhibition processes; this model provides an estimate of the time needed to cancel a planned movement. Response monitoring was assessed by the reaction time (RT) adjustments based on trial history. Like SZ patients, BP patients needed more time to cancel a planned movement. The two pa...
Endorsing the conceptual clarity of Nachev and Hacker, we offer an alternative perspective on int... more Endorsing the conceptual clarity of Nachev and Hacker, we offer an alternative perspective on intention and action that focuses on consequences instead of the antecedents of action. We propose that given many-to-one mapping of brain states to body movements, the brain processes that monitor action consequences offer a reconciliation of intentional reasons with neural causes. This proposal offers an enriched compatibilist position providing useful leverage on questions of responsibility and culpability.
The neural link between a sensory signal and its behavioral report was investigated in macaques t... more The neural link between a sensory signal and its behavioral report was investigated in macaques trained to locate an intermittently detectable visual target. Neurons in the frontal eye field, an area involved in converting the outcome of visual processing into motor ...
To determine whether visual discrimination in macaque frontal eye field (FEF) is contingent on sa... more To determine whether visual discrimination in macaque frontal eye field (FEF) is contingent on saccade planning, unit activity was recorded in two monkeys during blocked go and no-go visual search trials. The eye movements made by monkeys after correct no-go trials, in addition to an attenuation of the visual responses in no-go trials compared with go trials, indicated that covert saccade planning was effectively discouraged. During no-go search trials, the activity of the majority of neurons evolved to signal the location of the oddball stimulus. The degree and time course of the stimulus discrimination process observed in no-go trials was not different from that observed in go trials. We conclude that the discrimination of a salient visual stimulus reflected by FEF neurons is not contingent on saccade production but rather may reflect the outcome of an automatic visual selection process.
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Papers by Jeffrey Schall