Measurement Of Visual Pathway Functions Based On SSVEP

The primate visual system has three pathways: the Magnocellular pathway,the Parvocellular pathway,and the Koniocellular pathway.These visual pathways process information in parallel,and contribute to characterizing the visual scene’s temporal and spatial frequency properties.However,it is not clear what the optimal temporal and spatial frequency driving different visual pathways are.And driving these pathways by defining stimuli in the laboratory has become an important issue.The exploring of this issue has both clinical and practical implications: first,some cognitive functions are linked to specific pathways;second,patients suffering from certain disorders may have some degree of impairment in specific pathways.Therefore,based on the steady-state visual evoked potentials(SSVEPs),we measured the brain responses to achromatic and chromatic stimuli under various temporal and spatial frequencies in two experiments for finding and discussing the optimal temporal and spatial frequency that can be used to drive different pathways,with the aim of establishing an effective method for monitoring the function of visual pathways.In the first study,we investigated the optimal temporal characteristics of three visual pathways.The researchers created the DKL color space based on the property that Magnocellular cells,Parvocellular cells,and Koniocellular cells receive signals from different linear combinations of cones,respectively.The stimuli in this study were sampled from the L+M,L-M,and S-(L+M)axis in DKL color space,flickering at various temporal frequencies(1.5,3.0,5.0,7.5,15.0,and 30.0 Hz)to induce SSVEPs from the occipital regions of the brain.Results showed that SSVEPs evoked at 30 Hz better characterized responses to L+M;SSVEPs evoked at 15 Hz better characterized responses to L-M;while SSVEPs evoked at 1.5 Hz or 3 Hz better characterized responses to S-(L+M).The second study aimed to simultaneously explore the optimal spatiotemporal characteristics of three visual pathways.We tested the checkboard-like stimuli modulated by L+M,L-M,and S-(L+M)axis at three temporal frequencies(3,15,vs.30 Hz),at six spatial frequencies(0.2,1.0,2.0,3.0,4.0,vs.8.0 cycles/degree),and recorded the SSVEPs from the occipital lobe.The results showed that SSVEPs evoked at a temporal frequency of 15 Hz or 30 Hz and a spatial frequency of 4cycles/degree better characterized responses to L+M;SSVEPs evoked at a temporal frequency of 15 Hz and a spatial frequency of 0.2 cycles/degree better characterized responses to L-M;SSVEPs evoked at a temporal frequency of 3 Hz and a spatial frequency of approximately 1 cycle/degree better characterized responses to S-(L+M).In summary,we suggest that higher temporal frequency(30 Hz)and higher spatial frequency(4 cycles/degree)may be the optimal temporal and spatial frequency for driving the Magnocellular pathway,and medium temporal frequency(15 Hz)and lower spatial frequency(0.2 cycles/degree)may be the optimal temporal and spatial frequency for driving the Parvocellular pathway,and low temporal frequency(3 Hz)and medium spatial frequency(1 cycles/degree)may be the optimal temporal and spatial frequency for driving the Koniocellular pathway.In addition,this study may,to some extent,provide a scheme for measuring the contribution of visual pathways to cognitive function and be applied as a clinical tool for the detection of certain pathologies.