The neural basis of form and form-motion integration from static and dynamic translational Glass patterns: A rTMS investigation

Abstract

A long-held view of the visual system is that form and motion are independently analysed. However, there is physiological and psychophysical evidence of early interaction in the processing of form and motion. In this study, we used a combination of Glass patterns (GPs) and repetitive Transcranial Magnetic Stimulation (rTMS) to investigate in human observers the neural mechanisms underlying form-motion integration. GPs consist of randomly distributed dot pairs (dipoles) that induce the percept of an oriented stimulus. GPs can be either static or dynamic. Dynamic GPs have both a form component (i.e., orientation) and a non-directional motion component along the orientation axis. GPs were presented in two temporal intervals and observers were asked to discriminate the temporal interval containing the most coherent GP. rTMS was delivered over early visual area (V1/V2) and over area V5/MT shortly after the presentation of the GP in each interval. The results showed that rTMS applied over early visual areas affected the perception of static GPs, but the stimulation of area V5/MT did not affect observers' performance. On the other hand, rTMS was delivered over either V1/V2 or V5/MT strongly impaired the perception of dynamic GPs. These results suggest that early visual areas seem to be involved in the processing of the spatial structure of GPs, and interfering with the extraction of the global spatial structure also affects the extraction of the motion component, possibly interfering with early form-motion integration. However, visual area V5/MT is likely to be involved only in the processing of the motion component of dynamic GPs. These results suggest that motion and form cues may interact as early as V1/V2.

Reevaluating hMT+ and hV4 functional specialization for motion and static contrast using fMRI-guided repetitive transcranial magnetic stimulation

“…The effects observed for stimulation of hMTþ may be mediated by direct impairment of functional contrast perception in hMTþ in line with a role of MT neurons in various aspects of static contrast perception (T. D. Albright, 1984). rTMS suggests that involvement of hMTþ in global spatial tasks for static stimuli is unlikely (Pavan et al, 2017). It is possible that the effect of rTMS on contrast perception is mediated by ventral regions via some form of cortical cross-connectivity in line with the observation that direct stimulation of hV4 produces the larger effect.…”

“…Motion perception has proven particularly amenable to study via rTMS (Walsh et al, 1998;Cowey, Campana, Walsh, & Vaina, 2006;McKeefry et al, 2008;Stevens, McGraw, Ledgeway, & Schluppeck, 2009;McKeefry, Burton, & Morland, 2010;Waterston & Pack, 2010;Kaderali, Kim, Reynaud, & Mullen, 2015;Liu & Pack, 2017;Pavan, Ghin, Donato, Campana, & Mather, 2017;Strong et al, 2017). We used global motion stimuli in order to best target area hMTþ given that global motion requires signal integration across all elements of the stimulus, and area hMTþ is known to play a principal role in the spatial integration of local motion to reveal global motion direction (Born & Bradley, 2005).…”

Implied Motion From Form Shows Motion Aids the Perception of Global Form in Amblyopia

“…8,10,20 Moreover, these studies suggest a larger role for motion processing areas in decoding global implied motion from dynamic Glass patterns. 8,10,20 The influence of motion processing areas in processing dynamic Glass patterns is further supported by physiologic and imaging studies in monkeys and humans that report similar activation of motion processing area MT+ by real motion in RDKs and implied motion in dynamic Glass patterns. 7,13 Our results challenge the proposed dorsal stream vulnerability in developmental disorders such as amblyopia, where dorsal stream functions such as motion processing are reported to have a greater deficit than those of the ventral stream such as the processing of global form.…”

“…[37][38][39][40] For dynamic Glass patterns, the local processing of orientation would be similar to that of static Glass patterns while the overall implied motion is processed at higher extrastriate areas such as MT/MST. 20 In line with this, the internal equivalent noise (σ eq ) represents the uncertainty of the orientation processing mechanism at a local level (V1/V2), while the efficiency parameter represents the ability of the visual system to integrate local cues to provide the overall implied motion of the whole pattern, occurring at the extrastriate areas (MT, V4). 21,36 In the current study, we designed an experiment using dynamic Glass patterns with a range of overall dipole orientation variances, which served as external noise to provide a systematic account of how different levels of processing (i.e., local versus global) affect the performance in form perception (orientation discrimination) when motion perception is induced at the same time in amblyopia.…”

“…More recent studies show that similar mechanisms might also be present at higher cortical processing areas such as MT and MST. 8,10 Based on these findings, it has been proposed that the local processing (orientation of dipoles) of dynamic Glass patterns could occur by interaction at early cortical areas V1/V2, [13][14][15][16][17][18] while motion and form interaction at extrastriate areas of MT, V4 8,10,13,19,20 could be responsible for the global perception of implied motion.…”