Computation of the luminance and pattern components of the bar pattern electroretinogram

Abstract

Pattern onset electroretinograms (PERGs) were recorded from four normal subjects. Square-wave gratings of 75% contrast were presented in three approximately contiguous, concentric zones of outer angular radius, 5.1 degrees, 12.6 degrees, and 23.6 degrees. The zones were calculated to give equal numbers of ganglion cell receptive fields. The recorded PERGs were considered to include luminance and pattern components which have low and bandpass spatial tuning functions respectively. These components combine in the PERG to produce a broad spatial tuning characteristic. The amplitude of PERGs in response to low spatial frequency stimuli is widely reported to be linearly related to contrast. The retinal illuminance response at every spatial frequency was computed from the eye's modulation transfer function. This function characterizes the reduction in contrast that occurs because of optical degradation. The computed retinal illuminance response was subtracted from the PERG waveform and a pattern-specific response was revealed. The latter had a highly tuned bandpass function which peaked at higher spatial frequencies than the PERG at corresponding peripheral angles.

The effects of image degradation on retinal illuminance and pattern responses to checkerboard stimuli

“…In our earlier contribution, however, they were shown to be significant in the case of square-wave grtings (Thompson and Drasdo, 1987). It emerges that these effects are even more important when checkerboard patterns are used, since the harmonics in the pattern inevitably result in greater reductions in retinal contrast.…”

“…If the illumi- nance response is proportional to the stimulus contrast, then its contribution to the PERG elicited by checks of smaller angular subtense could be calculated from that at a large angular subtense by simply multiplying the signal by the attenuation factor of the temporal contrast function. This signal could then be subtracted from the PERG to extract the pattern-specific response, provided that there was no significant difference in latency of the luminance response with different contrasts as in the previously reported case for square-wve gratings (Thompson and Drasdo, 1987). Experimental evidence suggests that this is the case, for although the PERG changes in latency with spatial frequency, it does not appear to change systematically with differences in contrast for the larger check sizes.…”

“…4). The method is more fully described in the earlier study of Thompson and Drasdo (1987), in which square-wave gratings instead of checkerboards were used. definition; those from the small central zone had the lowest amplitude and noisiest waveforms although they were still clearly discernible.…”

Pattern Onset ERGs and VEPs Produced by Patterns Arising From Light Increment and Decrement

“…Similar results were previously reported by Arden and Vaegan and others. [17][18][19] This difference was not found to be significant when patterns arose from gray or white backgrounds (light decrement); however, in response to a light increment, onset amplitudes were significantly higher than the corresponding offset response (P < 0.001, Fig. 7).…”

“…The check size used in this study (60 0 ) might be the cause of this, as the amplitude of the offset response exhibits low-pass spatial tuning with larger amplitudes encountered using big check sizes. 18,19,23 Another possibility is that the offset response is driven more by temporal contrast than the onset response at this spatial frequency, resulting in different-sized components. 28 Furthermore, in this study, a substantial offset response was elicited only if the temporal contrast of the stimulus was higher than 33%, that is, in the light increment condition and when stimuli were appearing from a gray background.…”