Abstract
PurposeTo study the effect of stimulus size and temporal frequency on the relative contribution of luminance and L-/M-cone opponent signals in the ERG.MethodsIn four healthy, color normal subjects, ERG responses to heterochromatic stimuli with sinusoidal, counter-phase modulation of red and green LEDs were measured. By inverse variation of red and green contrasts, we varied luminance contrast while keeping L-/M-cone opponent chromatic contrast constant. The first harmonic components in the full field ERGs are independent of stimulus contrast at 12 Hz, while responses to 36 Hz stimuli vary, reaching a minimum close to isoluminance. It was assumed that ERG responses reflect L-/M-cone opponency at 12 Hz and luminance at 36 Hz. In this study, we modeled the influence of temporal frequency on the relative contribution of these mechanisms at intermediate frequencies, measured the influence of stimulus size on model parameters, and analyzed the second harmonic component at 12 Hz.ResultsThe responses at all frequencies and stimulus sizes could be described by a linear vector addition of luminance and L-/M-cone opponent reflecting ERGs. The contribution of the luminance mechanism increased with increasing temporal frequency and with increasing stimulus size, whereas the gain of the L-/M-cone opponent mechanism was independent of stimulus size and was larger at lower temporal frequencies. Thus, the luminance mechanism dominated at lower temporal frequencies with large stimuli. At 12 Hz, the second harmonic component reflected the luminance mechanism.ConclusionsThe ERGs to heterochromatic stimuli can be fully described in terms of linear combinations of responses in the (magnocellular) luminance and the (parvocellular) L-/M-opponent retino-geniculate pathways. The non-invasive study of these pathways in human subjects may have implications for basic research and for clinical research.
Highlights
The electroretinogram (ERG) is an electrophysiological response of the retina to visual stimulation and is an important non-invasive clinical tool to study the functional integrity of the retina [1]
The contribution of the luminance mechanism increased with increasing temporal frequency and with increasing stimulus size, whereas the gain of the L-/M-cone opponent mechanism was independent of stimulus size and was larger at lower temporal frequencies
Luminance reflecting ERG responses to sine wave modulations are large at temporal frequencies of 30 Hz and higher [5, 7, 8] and with full field stimuli [9, 10], whereas cone opponent responses dominate at temporal frequencies below 16 Hz and with spatially restricted stimulus sizes up to about 70° in diameter
Summary
The electroretinogram (ERG) is an electrophysiological response of the retina to visual stimulation and is an important non-invasive clinical tool to study the functional integrity of the retina [1]. We suggest that diffuse bipolar cells are luminance sensitive similar to the parasol retinal ganglion cells (belonging to the magnocellular pathway) [5, 6]. Which of the two pathways dominates in the ERG response depends on the stimulus size and on its temporal frequency. Luminance reflecting ERG responses to sine wave modulations are large at temporal frequencies of 30 Hz and higher [5, 7, 8] and with full field stimuli [9, 10], whereas cone opponent responses dominate at temporal frequencies below 16 Hz and with spatially restricted stimulus sizes up to about 70° in diameter. The amplitudes of luminance reflecting ERGs, decrease strongly with decreasing stimulus size and distance to the fovea [9,10,11]
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