Neuronal Population Activity Underlying Multi-Stable Motion Perception
Perceptual multistability is established when the brain fails to reach a single interpretation of the input from the external world. In the visual modality, a number of ambiguous visual patterns have been described such as the Necker cube, motion plaids, and binocular rivalry. Multi-stable stimuli can provide unique insights into visual processing, as changes in perception are decoupled from changes in the stimulus. Single-neuron studies have shown that higher in the visual hierarchy firing rates increasingly correlate with perception. However, very little is known about the underlying population level mechanisms mediating the selection process. Ambiguous perception can be evoked both by static and moving visual stimuli. Previous studies at the single neuron level have described two classes of neurons involved in solving the aperture problem in the motion domain: neurons that respond to the single motion components irrespective of the global motion perception and those responding to the coherent global pattern [1, 2].
The aim of our project is to understand the underlying mechanisms of selective integration of local motion vectors into globally perceived patterns. To this end, we will use multi-stable motion displays that introduce spontaneous switches between different stimulus interpretations.
Our approach will try to address these questions at the population level by performing simultaneous high density multi-electrode recordings in hierarchically organized motion responsive areas (MT, MST, LIP) . We will use multistable motion stimuli and specifically moving plaids consisting of three superimposed gratings moving to different directions. These stimuli induce the perception of component and pattern motion simultaneously since any two component gratings bind together and are perceived to move in the opposite direction of the third grating component (see Fig 1).
Fig. 1: An example of multi-stable stimuli in the motion domain. (a) A plaid consisting of three square-wave components each translating at a different constant velocity (red, green and blue arrows). (b) Velocity space representation of the stimulus. For some velocity combinations, the three constraint lines coincide, leading to a stable percept of coherent motion with velocity A. (c) However, other velocity combinations are inconsistent with a single coherent motion. Under these conditions, observers experience multi-stable motion transparency. At any point in time, two components tend to combine to form a plaid moving in one direction (A, B or C), while the remaining component appears to move in a different direction. The perceptual grouping of the components changes periodically with prolonged viewing. Stimulus variables such as the contrast, spatial frequency and component velocities can be used to systematically modify the relative duration of different interpretations.
1 Movshon JA, Adelson EH, Gizzi MS, Newsome WT. (1985). The analysis of visual moving patterns. In: Pattern recognition mechanisms (Chagas C, Gatass R, Gross C, eds), New York: Springer. 117151.
2 Khawaja FA, Tsui JM, Pack CC. (2009). Pattern motion selectivity of spiking outputs and local field potentials in macaque visual cortex. J Neurosci 29: 1370213709, 2009.
3 Keliris, G.A., Logothetis, N.K., and Tolias, A.S. (2010). The role of the primary visual cortex in perceptual suppression of salient visual stimuli. J Neurosci 30: 12353-12365.