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  • Binocular interactions  (1)
  • Visually evoked potential  (1)
  • 1
    ISSN: 1432-1106
    Keywords: Visually evoked potential ; Amblyopia ; Pseudorandom modulation ; Temporal frequency ; Spatio-temporal interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The visually evoked potential was recorded in response to pseudorandom modulation of a uniform field and sine-wave gratings in humans with naturally occurring amblyopia. Analysis in the frequency domain showed similar temporal tuning when the nonamblyopic and amblyopic eye were stimulated with a uniform field and with spatial stimuli. Although most observers showed some reduction in the cortical response to stimulation of the amblyopic eye with uniform field modulation, all observers showed reductions in the response obtained for stimulation of the amblyopic eye with spatial stimuli. This decrease in the cortical response to stimulation of the amblyopic eye for sine-wave gratings was present at either the low and middle temporal frequencies or over the range of temporal frequencies tested, and was greater than that observed in those amblyopes who also showed reductions with uniform field modulation. Latency measures in the time domain showed increases in the response of the early components when the amblyopic eye was stimulated with a uniform field and with sine-wave gratings above 2 c/deg. These electrophysiological results confirm the results obtained psychophysically which suggest that although amblyopia is primarily a spatial anomaly, the response is influenced by the temporal attributes of the stimulus as well.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-2622
    Keywords: Binocular interactions ; Psychophysics ; Amblyopia and strabismus ; Dichoptic masking ; Binocular vision ; Contrast sensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Binocular interactions for grating patterns were investigated in humans with normal binocular vision and in humans with abnormal binocular visual experience due to strabismus and/or amblyopia via 1) comparison of monocular and binocular contrast thresholds; 2) interocular transfer of the threshold elevation aftereffect; and 3) dichoptic masking. Whereas the normal observers showed improved binocular over monocular contrast sensitivity (i.e., binocular summation) and substantial interocular transfer of the threshold elevation aftereffect, the abnormal observers showed an absence of binocular summation and no significant interocular transfer. The dichoptic masking experiments showed that a suprathreshold masking grating presented to one eye elevated the contrast threshold for gratings presented to the fellow eye, within a narrow range of spatial frequencies (about 1 octave wide at half height) and orientations, centered about the spatial frequency and orientation of the mask. The magnitude and bandwidth of this masking effect was similar in subjects with normal and abnormal binocular vision, occurring even when the masking grating was presented to the amblyopic eye. These effects depend upon the contrast of the masking grating. In individuals with normal binocular vision, a grating with subthreshold contrast presented to one eye reduces the contrast threshold for detection of gratings of similar spatial frequency and orientation presented to the fellow eye. No such subthreshold summation is evident in the amblyopic observers. We conclude that while strabismus and/or amblyopia disrupted the normal excitatory interactions between the two eyes, cortical inhibitory binocular connections were not disrupted.
    Type of Medium: Electronic Resource
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