Abstract
A widely held view of the visual system supported the perspective that the primate brain is organized in two main specialized streams, called the ventral and dorsal streams. The ventral stream is known to be involved in object recognition (e.g., form and orientation). In contrast, the dorsal stream is thought to be more involved in spatial recognition (e.g., the spatial relationship between objects and motion direction). Recent evidence suggests that these two streams are not segregated but interact with each other. A class of visual stimuli known as Glass patterns has been developed to shed light on this process. Glass patterns are visual stimuli made of pairs of dots, called dipoles, that give the percept of a specific form or apparent motion, depending on the spatial and temporal arrangement of the dipoles. In this review, we show an update of the neurophysiological, brain imaging, psychophysical, clinical, and brain stimulation studies which have assessed form and motion integration mechanisms, and the level at which this occurs in the human and non-human primate brain. We also discuss several studies based on non-invasive brain stimulation techniques that used different types of visual stimuli to assess the cortico-cortical interactions in the visual cortex for the processing of form and motion information. Additionally, we discuss the timing of specific visual processing in the ventral and dorsal streams. Finally, we report some parallels between healthy participants and neurologically impaired patients in the conscious processing of form and motion.
Highlights
It is generally claimed that motion perception in visual stimuli involves sensors selective to direction, while form perception involves neurons selective to orientation and size (Mishkin et al, 1983; Ungerleider and Haxby, 1994; Braddick et al, 2000)
We report in detail the spatial and temporal features of Glass patterns (GPs) that allow us to investigate the mechanisms of form and motion integration
The results showed that apparent GP motion direction is attracted toward dipole orientation, and GP orientation is repulsed from GP motion
Summary
It is generally claimed that motion perception in visual stimuli involves sensors selective to direction, while form perception involves neurons selective to orientation and size (Mishkin et al, 1983; Ungerleider and Haxby, 1994; Braddick et al, 2000). Apparent motion direction in dynamic GPs is perceived according to the orientation of dipoles For this reason, dynamic GPs have been used to investigate the neural basis of form and motion processing and, in particular, to assess the interaction between the ventral and dorsal streams. Dynamic GPs have been used to investigate the neural basis of form and motion processing and, in particular, to assess the interaction between the ventral and dorsal streams The perception of both static and dynamic GPs involves two main processing stages: firstly, the local processing that allows the detection of the orientation of the single dipoles, and secondly, the global processing that enables the extraction of the overall shape from the pooling of local orientation cues (Prazdny, 1984; Wilson and Wilkinson, 1998; Pei et al, 2005; Chen, 2009; Chung and Khuu, 2014). NIBS techniques are useful to investigate the mechanisms underlying form–motion integration for three reasons: (i) assess the functional specialization of various visual areas, (ii) assess the deployment over time of a specific visual function, and (iii) understand the heterogeneity of spatial and temporal properties of visual units selective to form/orientation and motion (Silvanto, 2013)
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