Fig. 4
From: Neural contrast sensitivity is not affected by myopic blur
The interferometric setup and psychophysical procedure for the neural contrast sensitivity assessment. (A) Schematic beam path of the optical system forming the interference fringes on the retina by using a spatial light modulator (SLM). A motorized aperture adjusts the diameter of the field stop blocking higher order maxima as a result of the SLM based approach splitting the light source into two via a phase mask. The background consisted of the same light spectrum as the stimulus (indicated here with a yellowish path) and was used for a better contrast control as the background was always visible with the stimulus being projected on top of the background light. The tunable lens was adjusted by each participant to have the two spots perfectly overlapping on the retina. An on-axis pupil camera was used to ensure optimal stimulus delivery throughout the experiment. (B) Each trial consisted of two intervals and was started by the participant. One interval contained the stimulus, the other one a blank and the participant had to report the stimulus (signal) interval via a button press (2-Interval forced choice). The two intervals were accompanied by two tones and separated by an inter stimulus interval of 200 ms. (C) Exemplary experiment progression with QUEST for two runs. Stop criteria were a confidence interval for the current threshold estimate smaller than 0.15 (indicated by filled markers) and a minimum number of 30 trials. If the first criterion was not met after the first 30 trials, additional trials (up to 50 in total) were presented until a SD < 0.15 was reached. Runs not meeting the criterion after 50 trials were repeated.
