Normal discrimination of spatial frequency and contrast across visual hemifields in left-onset XXXX : Evidence against perceptual hemifield biases.

@entity1 @entity6572 @entity191
UNASSIGNED: Individuals with @entity191 ( @entity191 ) with symptom onset on the left side of the body ( @entity6572 ) show a mild type of left-sided visuospatial neglect, whereas those with right-onset (RPD) generally do not. The functional mechanisms underlying these observations are unknown. Two hypotheses are that the representation of left-space in @entity6572 is either compressed or reduced in salience. We tested these hypotheses psychophysically. @entity1 were 31 non-demented adults with @entity191 (15 @entity6572 , 16 RPD) and 17 normal control adults (NC). The spatial compression hypothesis was tested by showing two sinusoidal gratings, side by side. One grating's spatial frequency (SF) was varied across trials, following a staircase procedure, whereas the comparison grating was held at a constant SF. While fixating on a central target, @entity1 estimated the point at which they perceived the two gratings to be equal in SF. The reduced salience hypothesis was tested in a similar way, but by manipulating the contrast of the test grating rather than its SF. There were no significant differences between groups in the degree of bias across hemifields for SF discrimination or for contrast discrimination. Results did not support either the spatial compression hypothesis or the reduced salience hypothesis. Instead, they suggest that at this perceptual level, @entity6572 do not have a systematically biased way of representing space in the left hemifield that differs from healthy individuals, nor do they perceive stimuli on the left as less salient than stimuli on the right. Neglect-like syndrome in @entity6572 instead presumably arises from dysfunction of higher-order attention.
