Jeffrey Schall

schalljd@yorku.ca
http://www.psy.vanderbilt.edu/faculty/schall/

We practice the method of multiple hypotheses in research and in life. We avoid the blinding Influence of personal and petty affections. We debate ideas and respect people. We know that the best science flourishes in a liberal society. Indigenous & black lives & all lives matter.

We investigate these basic issues:

(1) We seek to understand how the brain selects the target for an eye movement. Pioneering the use of visual search with macaque monkeys, we discovered how the brain distinguishes a target from distractors and allocates attention. We are investigating the visual and cognitive influences on this attentional selection process and how it relates to the preparation of gaze shifts.
(2) We seek to understand how the brain regulates when to initiate a voluntary movement. Pioneering the use the stop signal (countermanding) task with monkeys, we discovered how particular neural circuits produce the random variation of response time and how responses are inhibited. We are investigating the neural and cognitive mechanisms of response production.

(3) We seek to understand how the brain monitors the consequences of actions. When monkeys make errors in visual search or countermanding tasks, we discovered that neurons in the medial frontal cortex register errors and success in the context of conflict. We are investigating the organization of these signals across neurons of different types across the cortical layers.

(4) In collaboration with Gordon Logan and Tom Palmeri, we seek to understand the computational principles underlying visual selection and response control. Pioneering the constraint of stochastic models of decision mechanisms with observed neural signals, we have explained how interacting circuits enable visual target selection and response production and inhibition. We are investigating how ensembles of accumulators make decisions and how visual salience arises.

(5) In collaboration with Alex Maier and Geoff Woodman, we seek to understand the neural origin of EEG measures indexing cognitive processes. We established that macaque monkeys produce homologues of the N2pc index of visual attention, the CDA index of visual working memory, and the error-related negativity (ERN) indexing performance monitoring. Pioneering the simultaneous sampling of neural signals across cortical layers with cranial EEG, we have discovered unexpectedly particular relationships between EEG and neural signals in certain cortical layers. We are investigating these relationships further to characterize the neural basis of EEG measures.

(6) In collaboration with Jorge Riera, we seek to understand the biophysical origin of EEG measures indexing cognitive processes. We formulate biophysical models of cortical pyramidal neurons to simulate electrical current patterns associated with different patterns of neural activity. We build biophysically realistic models of the brain in the head of monkeys to enable forward models of cranial voltage from cortical current patterns. We are investigating how visual area V4 and other areas contribute to the N2pc and how medial frontal areas contribute to the ERN.