The response of the amblyopic visual system to noise

Visual perception is limited by both the strength of the neural signals, and by the noise in the visual nervous system. Here we use one-dimensional white noise as input, to study the response of amblyopic visual system. We measured the thresholds for detection and discrimination of noise contrast. Using an N-pass reverse correlation technique, we derived classification images and estimated response consistency. Our results provide the first report of the sensitivity of the amblyopic visual system to white noise. We show that amblyopes have markedly reduced sensitivity for detecting noise, particularly at high spatial frequencies, and much less loss for discriminating suprathreshold noise contrast. Compensating for the detection loss almost (but not quite) equates performance of the amblyopic and normal visual system. The classification images suggest that the amblyopic visual system contains adjustable channels for noise, similar to those found in normal vision, but "tuned" to slightly lower spatial frequencies than in normal observers. Our N-pass results show that the predominant factor limiting performance in our task in both normal and amblyopic vision is internal random multiplicative noise. For the detection of white noise the raised thresholds of the amblyopic visual system can be attributed primarily to extra additive noise. However, for the discrimination of suprathreshold white noise contrast, there is surprisingly little additional deficit, after accounting for the visibility of the noise.