Neurons in V1, V2, and PMLS of Cat Cortex Are Speed Tuned But Not Acceleration Tuned: The Influence of Motion Adaptation

Abstract

. We studied neurons in areas V1, V2, and posteromedial lateral suprasylvian area (PMLS) of anesthetized cats, assessing their speed tuning using steps to constant speeds and acceleration and deceleration tuning using speed ramps. The results show that the speed tuning of neurons in all three cortical areas is highly dependent on prior motion history, with early responses during speed steps tuned to higher speeds than later responses. The responses to speed ramps are profoundly influenced by speed-dependent response latencies and ongoing changes in neuronal speed tuning due to adaptation. Acceleration evokes larger transient and sustained responses than subsequent deceleration of the same rate with this disparity increasing with ramp rate. Consequently, there was little correlation between preferred speeds measured using speed steps, acceleration or deceleration. From 146 recorded cells, the proportion of cells that were clearly speed tuned ranged from 69 to 100% across the three brain areas. However, only 13 cells showed good skewed Gaussian fits and systematic variation in their responses to a range of accelerations. Although suggestive of acceleration coding, this apparent tuning was attributable to a cell's speed tuning and the different stimulus durations at each acceleration rate. Thus while the majority of cells showed speed tuning, none unequivocally showed acceleration tuning. The results are largely consistent with an existing model that predicts responses to accelerating stimuli developed for macaque MT, which showed that the responses to acceleration can be decoded if adaptation is taken into account. However, the present results suggest future models should include stimulus-specific adaptation and speed-dependent response latencies.

Spatial phase sensitivity of complex cells in primary visual cortex depends on stimulus contrast

“…Brains were sectioned in the coronal plane by cryosectioning with a section width of 24 m. Slices were mounted on subbed slides and stained with thionin for Nissl substance Price et al 2006). Images of slices were digitized using 1-4 megapixel cameras attached to a microscope with ϫ4 magnification.…”

Direction and Contrast Tuning of Macaque MSTd Neurons During Saccades

“…It was previously noted that phasic responses of MSTd neurons are less selective for stimulus motion than tonic responses and that many cells generate sizable excitatory responses to motion in the antipreferred direction (Duffy and Wurtz 1991). Furthermore, 10°saccades induce retinal-slip velocities of 300 -400°/s and these fast speeds may have reduced the direction selectivity of MSTd neurons (although this does not appear to be the case for area MT; Price et al 2005). Figure 1B plots the preferred motion response against the antipreferred response for active motion.…”

“…Visual stimuli comprised random texture patterns formed of 0.8°dark or light squares spanning 77 ϫ 77°. They were rear-projected using a Mirage 2000 digital light projector (DLP; Christie Digital Systems, Cypress, CA) with resolution of 1,024 ϫ 1,024 pixels, frame rate of 96 Hz, and mean luminance 170 cd/m 2 (for issues relating to the DLP, see Price et al 2005). Texture contrast is defined as: Michelson contrast ϭ ([Luminance max Ϫ Luminance min ]/[Luminance max ϩ Luminance min ]) ϫ 100.…”

“…The imperceptibility of wide-field motion during saccades has been dubbed saccadic suppression. This phenomenon is not due to poor sensitivity for fast motion because stimuli with saccade-like speed and duration produce a powerful sense of movement during fixation (Ross et al 2001) and drive neurons at various stages in the visual system (e.g., subcortical: Price and Ibbotson 2001;cortical: Price et al 2005;Thiele et al 2002). It has been theorized that the loss of visual sensitivity during saccades is due to active attenuation of components within the visual system.…”

“…Another perplexing finding that has arisen from studies of saccadic suppression in MT and MSTd is that response latencies are reduced around the time of saccades (Ibbotson et al 2006(Ibbotson et al , 2008Price et al 2005;Thiele et al 2002). The response latencies to image motion generated during saccades can be as short as 30 ms, compared with around 70 ms in the absence of saccades (median values; Ibbotson et al 2007;Thiele et al 2002).…”