Abstract
We used magnetoencephalography (MEG) to determine whether increasingly complex forms constituted from the same elements (lines) activate visual cortex with the same or different latencies. Twenty right-handed healthy adult volunteers viewed two different forms, lines and rhomboids, representing two levels of complexity. Our results showed that the earliest responses produced by lines and rhomboids in both striate and prestriate cortex had similar peak latencies (40 ms) although lines produced stronger responses than rhomboids. Dynamic causal modeling (DCM) showed that a parallel multiple input model to striate and prestriate cortex accounts best for the MEG response data. These results lead us to conclude that the perceptual hierarchy between lines and rhomboids is not mirrored by a temporal hierarchy in latency of activation and thus that a strategy of parallel processing appears to be used to construct forms, without implying that a hierarchical strategy may not be used in separate visual areas, in parallel.
Highlights
Ever since the discovery of orientation-selective (OS) cells in V1 it has been supposed that they constitute the physiological building blocks for the elaboration of perceived forms and that, the brain analyses the visual world in hierarchical steps, each step constituting a more complex level of analysis than the preceding one (Hubel & Wiesel, 1962)
This supposition derives from the observation that OS cells have increasingly complex properties (Hubel & Wiesel, 1962), with simpler cells feeding into more complex ones in the same (Hubel & Wiesel, 1962) or in a ‘higher’ visual area (Hubel & Wiesel, 1965)
The anatomical pathways linking these areas with one another and with subcortical stations are, inevitably, less clear in the human brain, the assumption is that there, too, the properties of ‘higher’ form areas are traceable to the OS cells of V1 (e.g. Riesenhuber & Poggio, 1999), and oriented lines have been determined to be good stimuli for activating these human equivalents (Tootell et al, 1988; Kourtzi et al, 2003; Kamitani & Tong, 2006; Yacoub et al, 2008; Tong et al, 2012)
Summary
Ever since the discovery of orientation-selective (OS) cells in V1 (the primary visual cortex; Hubel & Wiesel, 1962, 1977) it has been supposed that they constitute the physiological building blocks for the elaboration of perceived forms and that, the brain analyses the visual world in hierarchical steps, each step constituting a more complex level of analysis than the preceding one (Hubel & Wiesel, 1962) This supposition derives from the observation that OS cells have increasingly complex properties (Hubel & Wiesel, 1962), with simpler cells feeding into more complex ones in the same (Hubel & Wiesel, 1962) or in a ‘higher’ visual area (Hubel & Wiesel, 1965). Given the parallel outputs in monkey from the pulvinar and the lateral geniculate nucleus to both V1 and areas of the prestriate cortex
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