Simple reaction times (RTs) are typically faster than choice reaction times and increase with unc... more Simple reaction times (RTs) are typically faster than choice reaction times and increase with uncertainty according to Hick's law. Here we show that smooth pursuit eye movement RTs show no effect of SR uncertainty while joystick tracking shows a step change between SRTand CRT, but no significant increases beyond two choices. The results suggest there is a benefit to pre-programming
To explore how eye and hand movements are controlled in a stop task, we introduced effector uncer... more To explore how eye and hand movements are controlled in a stop task, we introduced effector uncertainty by instructing subjects to initiate and occasionally inhibit eye, hand, or eye + hand movements in response to a color-coded foveal or tone-coded auditory stop signal. Regardless of stop signal modality, stop signal reaction time was shorter for eye movements than for hand movements, but notably did not vary with knowledge about which movement to cancel. Most errors on eye + hand stopping trials were combined eye + hand movements. The probability and latency of signal respond eye and hand movements corresponded to predictions of Logan and Cowan's (1984) race model applied to each effector independently.
Simple reaction times (RTs) are typically faster than choice reaction times and increase with unc... more Simple reaction times (RTs) are typically faster than choice reaction times and increase with uncertainty according to Hick's law. Here we show that smooth pursuit eye movement RTs show no effect of SR uncertainty while joystick tracking shows a step change between SRT and CRT, but no significant increases beyond two choices. The results suggest there is a benefit to pre-programming joystick tracking but not for smooth pursuit eye movements (SPEMs).
... In fact, the prevalence of grapheme-color synesthesia is currently unknown, with estimates br... more ... In fact, the prevalence of grapheme-color synesthesia is currently unknown, with estimates broadly ranging from 0.014% to 4.4% (Baron-Cohen, Burt, Smith-Laittan, Harrison, & Bolton, 1996; Rich,Bradshaw, & Mattingley, 2005; Simner, Mulvenna, Sagiv ... 290 / DOMINGO ET AL. ...
The stop-signal task has been used to study normal cognitive control and clinical dysfunction. It... more The stop-signal task has been used to study normal cognitive control and clinical dysfunction. Its utility is derived from a race model that accounts for performance and provides an estimate of the time it takes to stop a movement. This model posits a race between go and stop processes with stochastically independent finish times. However, neurophysiological studies demonstrate that the neural correlates of the go and stop processes produce movements through a network of interacting neurons. The juxtaposition of the computational model with the neural data exposes a paradox-how can a network of interacting units produce behavior that appears to be the outcome of an independent race? The authors report how a simple, competitive network can solve this paradox and provide an account of what is measured by stop-signal reaction time.
Humans and macaque monkeys adjust their response time adaptively in stop-signal (countermanding) ... more Humans and macaque monkeys adjust their response time adaptively in stop-signal (countermanding) tasks, responding slower after stop-signal trials than after control trials with no stop signal. We investigated the neural mechanism underlying this adaptive response time adjustment in macaque monkeys performing a saccade countermanding task. Earlier research showed that movements are initiated when the random accumulation of presaccadic movement-related activity reaches a fixed threshold. We found that a systematic delay in response time after stop-signal trials was accomplished not through a change of threshold, baseline, or accumulation rate, but instead through a change in the time when activity first began to accumulate. The neurons underlying movement initiation have been identified with stochastic accumulator models of response time performance. Therefore, this new result provides surprising new insights into the neural instantiation of stochastic accumulator models and the mechanisms through which executive control can be exerted.
Flexible behavior depends on the brain's ability to suppress a habitual response or to cancel a p... more Flexible behavior depends on the brain's ability to suppress a habitual response or to cancel a planned movement whenever needed. Such inhibitory control has been studied using the countermanding paradigm in which subjects are required to withhold an imminent movement when a stop signal appears infrequently in a fraction of trials. To elucidate the circuit mechanism of inhibitory control of action, we developed a recurrent network model consisting of spiking movement (GO) neurons and fixation (STOP) neurons, based on neurophysiological observations in the frontal eye field and superior colliculus of behaving monkeys. The model places a premium on the network dynamics before the onset of a stop signal, especially the experimentally observed high baseline activity of fixation neurons, which is assumed to be modulated by a persistent top-down control signal, and their synaptic interaction with movement neurons. The model simulated observed neural activity and fit behavioral performance quantitatively. In contrast to a race model in which the STOP process is initiated at the onset of a stop signal, in our model whether a movement will eventually be canceled is determined largely by the proactive top-down control and the stochastic network dynamics, even before the appearance of the stop signal. A prediction about the correlation between the fixation neural activity and the behavioral outcome was verified in the neurophysiological data recorded from behaving monkeys. The proposed mechanism for adjusting control through tonically active neurons that inhibit movement-producing neurons has significant implications for exploring the basis of impulsivity associated with psychiatric disorders.
Information about eye position is used to make accurate saccades to stimuli in the environment. T... more Information about eye position is used to make accurate saccades to stimuli in the environment. This study addressed the question of whether eye position is used in making perceptual judgments of the relative spatial locations of two successively presented visual targets. ...
Motion is a potent sub-modality of vision. Motion cues alone can be used to segment images into f... more Motion is a potent sub-modality of vision. Motion cues alone can be used to segment images into figure and ground and break camouflage. Specific patterns of motion support vivid percepts of form, guide locomotion by specifying directional heading and the passage of objects, and in case of an impending collision, the time to impact. Visual motion also drives smooth pursuit eye movements (SPEMs) that serve to stabilize the retinal image of objects in motion.
Current hypotheses about the mechanisms of executive control have been developed largely in the d... more Current hypotheses about the mechanisms of executive control have been developed largely in the domain of human subjects performing tasks involving response interference (such as Stroop or flanker tasks) or reinforcement learning. Distinguishing between alternative hypotheses about executive control has hinged on articulating the relationship (or lack thereof) between monitoring errors, reinforcement feedback, and response conflict. We will review research on the neurophysiological mechanisms observed in macaque monkeys performing a countermanding (stop signal) task with saccadic eye movements. Key insights include elucidation of how the brain controls whether and when a movement will be initiated, demonstration of the coexistence of error, reinforcement, and conflict signals in the medial frontal lobe, and demonstration of a mechanism by which the medial frontal lobe can influence motor structures to adapt performance. These insights grew out of a synthesis of conceptual frameworks and a coordination of neurophysiological, psychophysical, and mathematical modeling techniques.
Background: Cognitive control deficits are pervasive in individuals with schizophrenia (SZ) and a... more Background: Cognitive control deficits are pervasive in individuals with schizophrenia (SZ) and are reliable predictors of functional outcome, but the specificity of these deficits and their underlying neural mechanisms have not been fully elucidated. The objective of the present study was to determine the nature of response inhibition and response monitoring deficits in SZ and their relationship to symptoms and social and occupational functioning with a behavioral paradigm that provides a translational approach to investigating cognitive control.
Simple reaction times (RTs) are typically faster than choice reaction times and increase with unc... more Simple reaction times (RTs) are typically faster than choice reaction times and increase with uncertainty according to Hick's law. Here we show that smooth pursuit eye movement RTs show no effect of SR uncertainty while joystick tracking shows a step change between SRTand CRT, but no significant increases beyond two choices. The results suggest there is a benefit to pre-programming
To explore how eye and hand movements are controlled in a stop task, we introduced effector uncer... more To explore how eye and hand movements are controlled in a stop task, we introduced effector uncertainty by instructing subjects to initiate and occasionally inhibit eye, hand, or eye + hand movements in response to a color-coded foveal or tone-coded auditory stop signal. Regardless of stop signal modality, stop signal reaction time was shorter for eye movements than for hand movements, but notably did not vary with knowledge about which movement to cancel. Most errors on eye + hand stopping trials were combined eye + hand movements. The probability and latency of signal respond eye and hand movements corresponded to predictions of Logan and Cowan's (1984) race model applied to each effector independently.
Simple reaction times (RTs) are typically faster than choice reaction times and increase with unc... more Simple reaction times (RTs) are typically faster than choice reaction times and increase with uncertainty according to Hick's law. Here we show that smooth pursuit eye movement RTs show no effect of SR uncertainty while joystick tracking shows a step change between SRT and CRT, but no significant increases beyond two choices. The results suggest there is a benefit to pre-programming joystick tracking but not for smooth pursuit eye movements (SPEMs).
... In fact, the prevalence of grapheme-color synesthesia is currently unknown, with estimates br... more ... In fact, the prevalence of grapheme-color synesthesia is currently unknown, with estimates broadly ranging from 0.014% to 4.4% (Baron-Cohen, Burt, Smith-Laittan, Harrison, & Bolton, 1996; Rich,Bradshaw, & Mattingley, 2005; Simner, Mulvenna, Sagiv ... 290 / DOMINGO ET AL. ...
The stop-signal task has been used to study normal cognitive control and clinical dysfunction. It... more The stop-signal task has been used to study normal cognitive control and clinical dysfunction. Its utility is derived from a race model that accounts for performance and provides an estimate of the time it takes to stop a movement. This model posits a race between go and stop processes with stochastically independent finish times. However, neurophysiological studies demonstrate that the neural correlates of the go and stop processes produce movements through a network of interacting neurons. The juxtaposition of the computational model with the neural data exposes a paradox-how can a network of interacting units produce behavior that appears to be the outcome of an independent race? The authors report how a simple, competitive network can solve this paradox and provide an account of what is measured by stop-signal reaction time.
Humans and macaque monkeys adjust their response time adaptively in stop-signal (countermanding) ... more Humans and macaque monkeys adjust their response time adaptively in stop-signal (countermanding) tasks, responding slower after stop-signal trials than after control trials with no stop signal. We investigated the neural mechanism underlying this adaptive response time adjustment in macaque monkeys performing a saccade countermanding task. Earlier research showed that movements are initiated when the random accumulation of presaccadic movement-related activity reaches a fixed threshold. We found that a systematic delay in response time after stop-signal trials was accomplished not through a change of threshold, baseline, or accumulation rate, but instead through a change in the time when activity first began to accumulate. The neurons underlying movement initiation have been identified with stochastic accumulator models of response time performance. Therefore, this new result provides surprising new insights into the neural instantiation of stochastic accumulator models and the mechanisms through which executive control can be exerted.
Flexible behavior depends on the brain's ability to suppress a habitual response or to cancel a p... more Flexible behavior depends on the brain's ability to suppress a habitual response or to cancel a planned movement whenever needed. Such inhibitory control has been studied using the countermanding paradigm in which subjects are required to withhold an imminent movement when a stop signal appears infrequently in a fraction of trials. To elucidate the circuit mechanism of inhibitory control of action, we developed a recurrent network model consisting of spiking movement (GO) neurons and fixation (STOP) neurons, based on neurophysiological observations in the frontal eye field and superior colliculus of behaving monkeys. The model places a premium on the network dynamics before the onset of a stop signal, especially the experimentally observed high baseline activity of fixation neurons, which is assumed to be modulated by a persistent top-down control signal, and their synaptic interaction with movement neurons. The model simulated observed neural activity and fit behavioral performance quantitatively. In contrast to a race model in which the STOP process is initiated at the onset of a stop signal, in our model whether a movement will eventually be canceled is determined largely by the proactive top-down control and the stochastic network dynamics, even before the appearance of the stop signal. A prediction about the correlation between the fixation neural activity and the behavioral outcome was verified in the neurophysiological data recorded from behaving monkeys. The proposed mechanism for adjusting control through tonically active neurons that inhibit movement-producing neurons has significant implications for exploring the basis of impulsivity associated with psychiatric disorders.
Information about eye position is used to make accurate saccades to stimuli in the environment. T... more Information about eye position is used to make accurate saccades to stimuli in the environment. This study addressed the question of whether eye position is used in making perceptual judgments of the relative spatial locations of two successively presented visual targets. ...
Motion is a potent sub-modality of vision. Motion cues alone can be used to segment images into f... more Motion is a potent sub-modality of vision. Motion cues alone can be used to segment images into figure and ground and break camouflage. Specific patterns of motion support vivid percepts of form, guide locomotion by specifying directional heading and the passage of objects, and in case of an impending collision, the time to impact. Visual motion also drives smooth pursuit eye movements (SPEMs) that serve to stabilize the retinal image of objects in motion.
Current hypotheses about the mechanisms of executive control have been developed largely in the d... more Current hypotheses about the mechanisms of executive control have been developed largely in the domain of human subjects performing tasks involving response interference (such as Stroop or flanker tasks) or reinforcement learning. Distinguishing between alternative hypotheses about executive control has hinged on articulating the relationship (or lack thereof) between monitoring errors, reinforcement feedback, and response conflict. We will review research on the neurophysiological mechanisms observed in macaque monkeys performing a countermanding (stop signal) task with saccadic eye movements. Key insights include elucidation of how the brain controls whether and when a movement will be initiated, demonstration of the coexistence of error, reinforcement, and conflict signals in the medial frontal lobe, and demonstration of a mechanism by which the medial frontal lobe can influence motor structures to adapt performance. These insights grew out of a synthesis of conceptual frameworks and a coordination of neurophysiological, psychophysical, and mathematical modeling techniques.
Background: Cognitive control deficits are pervasive in individuals with schizophrenia (SZ) and a... more Background: Cognitive control deficits are pervasive in individuals with schizophrenia (SZ) and are reliable predictors of functional outcome, but the specificity of these deficits and their underlying neural mechanisms have not been fully elucidated. The objective of the present study was to determine the nature of response inhibition and response monitoring deficits in SZ and their relationship to symptoms and social and occupational functioning with a behavioral paradigm that provides a translational approach to investigating cognitive control.
Uploads
Papers by Leanne Boucher