The Effects of Temporal Modulation on the Oblique Effect in Humans

Contrast thresholds were measured for vertical and oblique grating patterns. As shown previously, at higher spatial frequencies sensitivity for vertical is much greater than that for oblique. Present results show that this difference in sensitivity is found only with low rates of temporal modulation; with higher temporal frequencies this orientation difference disappears. Moreover, when contrast thresholds are based on the perception of flicker, vertical and oblique sensitivities are essentially identical even at low flicker rates. These results indicate that the so-called ‘oblique effect’ is confined to mechanisms with poor temporal resolving power, probably the sustained channels which have been studied psychophysically and neurophysiologically by others.