The Research On The Coding And Decoding Color Information In The Optic Tectum Of Pigeon

In a large number of visual information,color is a natural property that all the objects and environment own.Studying the coding of color information in the visual system has a heuristic significance for us to understand the working mechanism in the visual system,and studying the decoding of color information has a wide application prospect for the effective use of biological vision system.Pigeons have an advanced capacity for color perception,but the study of its vision system is still in its infancy.In this paper,sober pigeons were chosen as model animals,and our study was focused on the key structure for processing color information in the tectofugal pathway:the Optic Tectum(OT),and exploring the receptive field properties,coding and decoding rules of the OT neurons by acquiring spikes firing of the OT neurons under different color stimuli.The main work and results of our study are as follows:Firstly,according to the types of color-sensitive cells in the retina of the pigeon,checkerboard stimulation patterns with red,green,blue,black,and white blank flashes on a gray background were designed,and spikes-triggered average with Gaussian function fitting is applied to analysis spikes firing of the OT neurons.The results showed that the positions and extents of the receptive fields under different color stimuli were similar,but slightly different.The distances between the centers of the receptive fields under black and white stimuli were<0.5°,whereas the distances between red,green,blue and black stimuli were from 1–1.7°.The areas of the receptive fields under the five different color stimuli were between 10 and15°~2.secondly,according to the types of color-sensitive cells in the retina and the response characteristics of the OT neurons,flashing color blocks with red,green,blue,black,white were designed,and the response characteristics to per stimulus time histogram(PSTH)when five color stimuli appeared and were removed were extracted,then three characteristic parameters of the mean response,the maximum response time and the response band in PSTH were extracted for statistic.The results showed:First,when colors appeared,the mean responses to blue and black stimuli were stronger than were those to other colors,the white stimulus had the smallest maximum response time and the narrowest response band,and red stimulus had the largest maximum response time and the widest response band.Second,when the colors were removed,the blue and black stimuli had the stronger mean responses,the larger maximum response times,and the larger response band,followed by the red stimulus;there was almost no response to the white stimulus.The OT neurons had almost no response whether the green color stimulus appeared or was removed.Third,almost all of the OT neurons were on-off type to blue and black stimuli,87.5%were on-off type to the red stimulus,and 62.5%were on type to the white stimulus.Four,according to the response characteristics of the OT neurons in response to red,green,blue,we concluded that different OT neurons had different response characteristics under the same color stimulus,but one of OT neurons nearly had the fixed response characteristics under one color stimulus in repeated experiments,so that we pointed our view:the OT neurons coding color information in population.Finally,based on the view of population coding,we extracted the response characteristics to PSTH of the OT neurons in population,then linear and nonlinear dimensionality reduction methods PCA and ISOMAP were applied to integrated the features,then PNN and SVM were applied to classify three chromatic stimuli of red,green,blue and five color stimuli of red,green,blue,black,white in the gray background.The results showed that:three chromatic stimuli were classified well no matter any dimensionality reduction method and any classification method were applied,and recognition rates reached almost 100%.Then two achromatic stimuli of black and white were added,and the results showed that:First,red,green,white stimuli were recognized well under any method,and the mean recognition rate were above 90%with small variance.Second,blue and black stimuli were recognized bad with the reason that the response characteristics to PSTH of the OT neurons under blue and black color stimuli were almost overlapping and this caused that some blue color stimuli were identified as black color stimuli while some black ones were identified as blue ones.