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The temporal modulation transfer function of the human ERG and VECP
IUPS-ISCERG
Symposium Papers
1201
percentage of recall of information presented to either or both eyes used in the VER averaging. A continuum of eye dominance was found in the normal sample with behavioral measures. Some subjects recalled dissimilar information from each eye equally (about 40-45 per cent). At the unequal contribution end of the continuum, some normals had differences as great as 85 per cent from one eye and 15 per cent from the other. Recall of letters and numbers were similar, and the effect was relatively independent of the type of information being presented to the opposite eye as long as it was disparate. The inhibition of information from one eye was almost as great in some of the latter normals as that from amblyopic eyes. However, recall of information presented monocularly was always 95100 per cent for normal eyes and less than 30 per cent for amblyopic eyes. Results clearly demonstrate that assignment of a single dominance constant across a normal population is inappropriate; that impairment in binocular functioning of some normals approaches that of amblyopic subjects in these tasks; and that amblyopic suppression is increased in binocular vision. Results with the VER measures were equivocal, but will be included in the paper, with a discussion of central mechanisms in normal and amblyopic vision.
22 The temporal modulation transfer function of the human ERG and VECP C. R. CAVONKJSand C. E. STERNHEIM. UnirTersityof Munich, Institute for Medical Optics,
8 Miinchen 13, Barbarastrasse 16, Germany, and Department of Psychology, Unirersity of Marylatid, U.S.A. ERG and visual evoked cortical potentials (VECP) were elicited by a 20” circular target filled with a 0.75 cycle/deg horizontal square wave grating. Alternate grating bars were sinusoidally modulated 180” out of phase so that mean retinal illumination was constant (2920 photopic trolands at 620 nm). This stimulus pattern appears to elicit purely photopic responses since different wavelength stimuli caused identical (approximately sinusoidal) ERG responses when equated for photopic luminance. Temporal frequencies from 3 to 60 Hz were presented. At each frequency, peak-to-peak ERG and VECP amplitudes were plotted vs. log per cent modulation, yielding Linear functions. These were extrapolated to predict the modulation which would have given zero PV response at each frequency. When this log criterion modulation is plotted against log temporal frequency, the high frequency slopes of the VECP MTF closely resemble the observers’ de Lange functions (psychophysical MTF), with a slope of about 12.5 dB/octave. At low frequencies, the ERG is less sensitive than either the psychophysical or cortical MTF, but the ERG slope is less steep (about 3 dB/octave) and its high frequency cut-off is higher than the psychophysical or cortical cut-off. N.S.F. grant No. GB4266.
Symposium Papers
1201
percentage of recall of information presented to either or both eyes used in the VER averaging. A continuum of eye dominance was found in the normal sample with behavioral measures. Some subjects recalled dissimilar information from each eye equally (about 40-45 per cent). At the unequal contribution end of the continuum, some normals had differences as great as 85 per cent from one eye and 15 per cent from the other. Recall of letters and numbers were similar, and the effect was relatively independent of the type of information being presented to the opposite eye as long as it was disparate. The inhibition of information from one eye was almost as great in some of the latter normals as that from amblyopic eyes. However, recall of information presented monocularly was always 95100 per cent for normal eyes and less than 30 per cent for amblyopic eyes. Results clearly demonstrate that assignment of a single dominance constant across a normal population is inappropriate; that impairment in binocular functioning of some normals approaches that of amblyopic subjects in these tasks; and that amblyopic suppression is increased in binocular vision. Results with the VER measures were equivocal, but will be included in the paper, with a discussion of central mechanisms in normal and amblyopic vision.
22 The temporal modulation transfer function of the human ERG and VECP C. R. CAVONKJSand C. E. STERNHEIM. UnirTersityof Munich, Institute for Medical Optics,
8 Miinchen 13, Barbarastrasse 16, Germany, and Department of Psychology, Unirersity of Marylatid, U.S.A. ERG and visual evoked cortical potentials (VECP) were elicited by a 20” circular target filled with a 0.75 cycle/deg horizontal square wave grating. Alternate grating bars were sinusoidally modulated 180” out of phase so that mean retinal illumination was constant (2920 photopic trolands at 620 nm). This stimulus pattern appears to elicit purely photopic responses since different wavelength stimuli caused identical (approximately sinusoidal) ERG responses when equated for photopic luminance. Temporal frequencies from 3 to 60 Hz were presented. At each frequency, peak-to-peak ERG and VECP amplitudes were plotted vs. log per cent modulation, yielding Linear functions. These were extrapolated to predict the modulation which would have given zero PV response at each frequency. When this log criterion modulation is plotted against log temporal frequency, the high frequency slopes of the VECP MTF closely resemble the observers’ de Lange functions (psychophysical MTF), with a slope of about 12.5 dB/octave. At low frequencies, the ERG is less sensitive than either the psychophysical or cortical MTF, but the ERG slope is less steep (about 3 dB/octave) and its high frequency cut-off is higher than the psychophysical or cortical cut-off. N.S.F. grant No. GB4266.