[Bandwidth measurement technique for spatial frequency channels in human visual system]

to determine the number of measurements required to obtain stable bandwidth values for spatial frequency channels (SFCs) in the human visual system.

Ten untrained, normal vision subjects 18-22 years old were presented with light pulses (flickers) with initial frequency of 10 Hz and then with a higher-than-initial and lower-than-initial frequency alternately at 1-sec intervals. The difference between flickers frequencies was gradually increased until the test subject determined his/her discrimination threshold. This threshold was assumed to represent the SFC bandwidth. Measured values were plotted on a coordinate system «SFC bandwidth - the number of measurement». The described procedure was repeated and a graph resulted showing SFC bandwidth as a function of Ni, where Ni is the number of i-th measurement and i = 1, 2, ..., k (k - the sequence number of measurement at which the transition process was completed and a quasi-stationary state achieved): ΔF=f(Ni). The number of measurements required to obtain stable SFC bandwidth values was determined from the number of measurements made during the transition process.

It has been found that to obtain stable bandwidth values for SFCs of the human visual system, 2 to 8 measurements are required (point estimate of the median for the given sample equaled 5).

The duration of a transition process to stable SFC bandwidth values is individual and this should be taken into account when assessing the visual system.