Spatial vision in adults and infants: a tribute to Russell Harter

To be recognized, the retinal image of an object must first be segregated from the retinal image of its surroundings. Luminance contrast is only one way by which an object can be rendered visible. Motion contrast alone, texture contrast alone, colour contrast alone and disparity contrast alone can also render an object visible. This paper notes that psychophysical studies of patients with brain lesions show that motion-defined form and luminance-defined form are processed separately and describes how magnetic (MEG) or electrical (VEP) recording can be used to compare brain responses to luminance-defined form, motion-defined form, colour-defined form, texture-defined form and disparity-defined form. At an early stage in visual processing, the retinal images of luminance-defined objects pass through neural filters, each of which is selectively sensitive to a limited range of orientations, spatial frequencies and temporal frequencies. The properties of individual filters can be isolated and quantified by means of the two-sinewave VEP approach. The two-sinewave method also allows binocular function to be tested objectively and its normality assessed quantitatively even when one or both eyes have low acuity. Evoked potential studies of visual development in human infants and studies of labile phenomena in adults are both facilitated by the speed of our VEP sweep method.