Direct evidence for encoding of motion streaks in human visual cortex

Abstract

Temporal integration in the visual system causes fast-moving objects to generate static, oriented traces (‘motion streaks’), which could be used to help judge direction of motion. While human psychophysics and single-unit studies in non-human primates are consistent with this hypothesis, direct neural evidence from the human cortex is still lacking. First, we provide psychophysical evidence that faster and slower motions are processed by distinct neural mechanisms: faster motion raised human perceptual thresholds for static orientations parallel to the direction of motion, whereas slower motion raised thresholds for orthogonal orientations. We then used functional magnetic resonance imaging to measure brain activity while human observers viewed either fast (‘streaky’) or slow random dot stimuli moving in different directions, or corresponding static-oriented stimuli. We found that local spatial patterns of brain activity in early retinotopic visual cortex reliably distinguished between static orientations. Critically, a multivariate pattern classifier trained on brain activity evoked by these static stimuli could then successfully distinguish the direction of fast (‘streaky’) but not slow motion. Thus, signals encoding static-oriented streak information are present in human early visual cortex when viewing fast motion. These experiments show that motion streaks are present in the human visual system for faster motion.

Interactions between motion and form processing in the human visual system

“…Thus, rapid retinal motion produces responses both in motion-selective cells tuned to that direction, and in orientation-selective cells tuned to an orientation aligned with the axis of the motion—the motion-streak. Psychophysical evidence from orientation detection and after-effects, as well as recent neuroimaging data, is consistent with the view that motion-streaks excite orientation-tuned cells in the human visual system (Alais et al, 2011; Apthorp et al, 2011, 2013). Geisler (1999) proposed that the outputs of motion- and orientation-selective cells are combined in visual cortex to create a “spatial motion-direction” (SMD) sensor tuned to both streak orientation and motion direction.…”

The interaction between orientation and motion signals in moving oriented Glass patterns

“…Albright (1984) investigated the orientation selectivity of 89 MT cells of macaque monkey and found that 29% of the cells exhibited an orientation preference that is roughly parallel to the preferred motion direction. More recently, a human brain imaging study by Apthorp et al (2013) showed that motion streaks are likely to be extracted at early stages of visual analysis, implying that motion and form, while seemingly separate, are processed and combined as early as the primary visual cortex. In addition, there is brain imaging and psychophysical evidence that early visual areas can encode and pool the sparse local orientation cues in translational GPs (Ohla et al, 2005;Ostwald et al, 2008;Mannion et al, 2009Mannion et al, , 2010Pavan et al, 2016).…”

The shape of motion perception: Global pooling of transformational apparent motion

“…Dynamic Glass patterns (a series of independently generated static Glass patterns shown in a fast temporal sequence) do not present a consistent motion energy signal but do give the impression of coherent motion consistent with the pattern type, showing the strong effect form cues can have on the perceived direction of motion (Ross et al, 2000). The perception of coherent motion in the absence of coherent motion energy suggests the form information in the Glass patterns causes the perceived axis of motion (Apthorp et al, 2013;Nankoo, Madan, Spetch, & Wylie, 2012).…”

“…Evidence suggests that the same global form mechanism is sensitive to shape information, and shape information derived from illusory displacement in perceived position (Dickinson, Han, Bell, & Badcock, 2010). Motion streaks, arising from the extended temporal integration period of neurons in early visual cortex, improve global motion discrimination (Edwards & Crane, 2007) and provides a form cue in the direction parallel to the motion signal, which can refine direction estimates (Apthorp et al, 2013;Barlow & Olshausen, 2004;Burr & Ross, 2002;Francis & Kim, 2001;Geisler, 1999;Ross, 2004;Ross, Badcock, & Hayes, 2000). Providing form cues indicating a closed contour also enhances recovery of the global motion direction compared to an open contour (Lorenceau & Alais, 2001;Lorenceau & Lalanne, 2008).…”