Visual Motion Analysis for Pursuit Eye Movements in Area MT of Macaque Monkeys

Abstract

We asked whether the dynamics of target motion are represented in visual area MT and how information about image velocity and acceleration might be extracted from the population responses in area MT for use in motor control. The time course of MT neuron responses was recorded in anesthetized macaque monkeys during target motions that covered the range of dynamics normally seen during smooth pursuit eye movements. When the target motion provided steps of target speed, MT neurons showed a continuum from purely tonic responses to those with large transient pulses of firing at the onset of motion. Cells with large transient responses for steps of target speed also had larger responses for smooth accelerations than for decelerations through the same range of target speeds. Condition-test experiments with pairs of 64 msec pulses of target speed revealed response attenuation at short interpulse intervals in cells with large transient responses. For sinusoidal modulation of target speed, MT neuron responses were strongly modulated for frequencies up to, but not higher than, 8 Hz. The phase of the responses was consistent with a 90 msec time delay between target velocity and firing rate. We created a model that reproduced the dynamic responses of MT cells using divisive gain control, used the model to visualize the population response in MT to individual stimuli, and devised weighted-averaging computations to reconstruct target speed and acceleration from the population response. Target speed could be reconstructed if each neuron's output was weighted according to its preferred speed. Target acceleration could be reconstructed if each neuron's output was weighted according to the product of preferred speed and a measure of the size of its transient response.

Connections of the Dorsomedial Visual Area: Pathways for Early Integration of Dorsal and Ventral Streams in Extrastriate Cortex

“…Thus, the inferred physiological association of DM with the medial circuit of the dorsal stream is perhaps best understood as a consequence of the fact that a large proportion of guided body movements depend on information contained in peripheral vision. Conversely, the expanded foveal representation in MT places this area in a better position to control tracking eye movements (Komatsu and Wurtz, 1988;Lisberger and Movshon, 1999).…”

Temporal dynamics of motion integration for the initiation of tracking eye movements at ultra-short latencies

“…Electrophysiological studies in monkey suggest that the short-latency tracking responses are mediated, in part, by area MST (Kawano et al, 1994). The main input to area MST is from area MT that is also involved in the visual motion processing for smooth tracking eye movements (Lisberger & Movshon, 1999). Neurons in area MT are activated by a wide range of, loosely speaking, second-order stimuli (Rodman & Albright, 1989;Albright, 1992;O'Keefe & Movshon, 1998).…”

Effects of Nicotine on Leading Saccades during Smooth Pursuit Eye Movements in Smokers and Nonsmokers with Schizophrenia

“…The SPEM response broadly involves: (a) the processing of retinal motion information (ie the movement of a target image on the retina); (b) the initiation of an oculomotor response based on retinal information, which can be modified by previous target motion information (Lisberger et al, 1987;Barnes et al, 2000); (c) the processing and integration of extraretinal motion signals generated by movement of the eyes (Turano and Heidenreich, 1999;Turano and Massof, 2001); the maintenance of pursuit based on a combination of predictive eye movements guided by extraretinal signals and corrective eye movements guided by retinal velocity and position error signals (Barnes and Asselman, 1991;van den Berg, 1988). Basic researchers have carefully described many of these processes and the neuronal substrates that underlie them in healthy human subjects (eg Braun et al, 1996;Petit et al, 1997;Berman et al, 1999;Schmid et al, 2001) and nonhuman primates (eg Lisberger and Movshon, 1999;Newsome et al, 1988;MacAvoy et al, 1991;Assad and Maunsell, 1995;Komatsu and Wurtz, 1989;Krauzlis, 2001;Suh et al, 2000).…”