The Neural Mechanism Of Motion And Form Interaction In Macaque Superior Temporal Sulcus

Visual information plays a vital role in our perception of the 3D environment.Especially,motion and form cues are essential component of visual information.Evidence show that,there are interactions between motion and form cues.Therefore,elucidation of this interaction is of great significance for our research on visual perception.Previous studies show that the motion and form cues are processed by the dorsal and ventral visual pathway separately in the visual cortex.However,recent studies show that,dorsal pathway also receives the form information input.Moreover,the psychophysics experiments on human show that both motion and form cues can affect the visual perception.In this project,we use the self-motion perception as the paradigm for studying the interaction between motion and form in the dorsal visual pathway.There are altogether 3 kinds of stimuli for simulation of self-motion: first,the motion cue only condition in which single random dots expand from the focus of expansion(FOE);second,the static Glass Pattern stimuli in the form only condition;third,the combined condition in which the dot pairs in the Glass Pattern expand from the motion FOE while keep their orientation to the form FOE.Single electrodes were used to record from the Superior Temporal Sulcus(STS)of awake macaques while they fixate on the center of the screen presenting visual stimuli.We looked into the following aspects in the STS area: 1)whether there exist form sensitive neurons;2)whether form affects motion processing;3)if interaction exists what exactly is the mechanism.The average firing rate of single neurons during stimulus time were calculated and categorized based on different visual stimuli conditions,and results are as follows:Among the 95 neurons recorded,altogether 54 cells(56.8%)are significantly tuned to motion FOEs in the motion only condition(p<0.05,one-way ANOVA),while the rest is not significantly tuned to motion only or form only stimuli.However,we found temporal modulation of form information in 14.7%(14/95)of neurons,with significant firing rate compared to baseline activity.Under combined conditions,the number of neurons with significant motion tuning increased from 54 to 75(79.0%),in which 24.1%(14/54)of neurons significantly tuned to both motion and form(p<0.05,two-way ANOVA).Therefore,although STS exhibit weak response to form alone,form still affects its motion processing,which indicates the possible modulation effect of form information in STS.Next,we looked into the following aspects of the motion tuning properties,for the quantification of the effects of form to motion processing: shifts of preferred FOE,modulation of firing rate and tuning width.Results are as follows: among these 54 motion significant neurons: 1)44.4%(24/54)showed shift of preferred directions;2)gain modulation of firing rate was found in 48.1%(26/54)of neurons;3)38.9%(2154)of the neurons had decreased motion tuning width in the congruent condition compared with motion only condition,which indicates the change of neurons' motion sensitivity as a result of form cues.To further prove this,we looked at the neurometric functions from narrow tuning data,the fine headings around 0°,and found that 35.3%(6/17)of neurons' thresholds decreased in the congruent combined condition,indicating that form affects motion discrimination sensitivity in STS.Lastly,Modulation Index(MI)was calculated to quantify the modulation,and were compared to the relative anterior-posterior position.It was found that the standard deviation of MI is larger in the more anterior neurons.These indicate the more heterogeneous modulations of form to motion cues in the more anterior part of STS.This project expands our knowledge about the visual processing,and also provides theoretical guidance to object recognition based on motion and form in Computer Vision.