Dynamic Engagement of Human Motion Detectors across Space-Time Coordinates

Abstract

Motion detection is a fundamental property of the visual system. The gold standard for studying and understanding this function is the motion energy model. This computational tool relies on spatiotemporally selective filters that capture the change in spatial position over time afforded by moving objects. Although the filters are defined in space-time, their human counterparts have never been studied in their native spatiotemporal space but rather in the corresponding frequency domain. When this frequency description is back-projected to spatiotemporal description, not all characteristics of the underlying process are retained, leaving open the possibility that important properties of human motion detection may have remained unexplored. We derived descriptors of motion detectors in native space-time, and discovered a large unexpected dynamic structure involving a Ͼ2ϫ change in detector amplitude over the first ϳ100 ms. This property is not predicted by the energy model, generalizes across the visual field, and is robust to adaptation; however, it is silenced by surround inhibition and is contrast dependent. We account for all results by extending the motion energy model to incorporate a small network that supports feedforward spread of activation along the motion trajectory via a simple gain-control circuit.

Natural motion trajectory enhances the coding of speed in primate extrastriate cortex

“…An interesting possibility is that the temporal context of the moving trajectory allows the history of the stimulus outside the receptive field to influence how information is processed when the stimulus is in the receptive field. Such mechanisms have been suggested by psychophysical studies 19 20 21 22 . Further studies are required to test this possibility.…”

Mechanisms of spectrotemporal modulation detection for normal- and hearing-impaired listeners

“…More specifically, prior psychophysical work has demonstrated that perceptual analyzers can be successfully characterized as oriented sensors (Adelson & Bergen, 1991), where orientation may be defined e.g. across space-space (Neri, 2015) or space-time (Burr et al, 1986; Neri, 2014b). More relevant to the present investigation, it has also demonstrated that noisy processes spanning different dimensions of the target stimulus, such as its native space-space or its orientation subspace, can be leveraged to probe the same perceptual operation and constrain a unique computational description of that operation (Neri, 2015).…”

Catching the voltage gradient—asymmetric boost of cortical spread generates motion signals across visual cortex: a brief review with special thanks to Amiram Grinvald

“…69,98 Indeed, characterizing human motion detectors in space-time coordinates 99 led to the discovery of a previously unknown brief increase in detector amplitude at motion onset. 100 The perceptual relevance of retinotopic encoding of motion trajectories in V1 (Ref. 101) was, furthermore, demonstrated using a "pathguided" apparent motion paradigm in combination with fMRI.…”