Retinal and post-retinal contributions to the quantum efficiency of the human eye

TL;DR

This study investigates how post-retinal neural processing affects the human eye's quantum efficiency, revealing that decision-related brain activity contributes to perceptual thresholds beyond retinal photon detection.

Contribution

It provides evidence that post-retinal neural processes significantly influence perceptual thresholds, extending understanding of human visual detection limits beyond retinal photon response.

Findings

Reaction times increase as photon number decreases.

EEG response latencies correlate with reaction times and stimulus intensity.

Post-retinal processing delays contribute to detection noise.

Abstract

The retina is one of the best known quantum detectors with rods able to respond to a single photon. However, estimates on the number of photons eliciting conscious perception, based on signal detection theory, are systematically above these values. One possibility is that post-retinal processing significantly contributes to the decrease in the quantum efficiency determined by signal detection. We carried out experiments in humans using controlled sources of light while recording EEG and reaction times. Half of the participants behaved as noisy detectors reporting perception in trials where no light was sent. DN subjects were significantly faster to take decisions. Reaction times significantly increased with the decrease in the number of photons. This trend was reflected in the latency and onset of the EEG responses over frontal and parietal contacts where the first significant differences in latency comparable to differences in reaction time appeared. Delays in latency of neural responses across intensities were observed later over visual areas suggesting that they are due to the time required to reach the decision threshold in decision areas rather than to longer integration times at sensory areas. Our results suggest that post-retinal processing significantly contribute to increase detection noise and thresholds, decreasing the efficiency of the retina brain detector system.