However, the widely accepted view is that the sensitivity fall-off at high temporal frequencies is due to early temporal filtering (e.g., Kelly,
1961,
1969; Roufs,
1972; Watson,
1986; Watson & Ahumada, Jr.,
1985), which should affect equivalent input noise, not calculation efficiency. Early temporal filtering would reduce the effective contrast of high temporal frequencies (Watson,
1986) and a contrast reduction gain affecting the signal and noise by the same proportion would have no effect on the signal-to-noise ratio and therefore should have no impact on contrast threshold in high noise (i.e., calculation efficiency, Pelli & Farell,
1999). Indeed, contrast threshold in high noise is known to be proportional to the noise contrast (slope of 1 in log-log coordinates, Pelli,
1981), so substantially reducing contrast at high temporal frequencies should have a direct impact on contrast threshold in low noise (i.e., sensitivity), but not in high noise (i.e., calculation efficiency), that is, it would affect equivalent input noise. As a result, Pelli's (
1990) finding that equivalent input noise is constant at high temporal frequencies seems incompatible with the widely accepted view that the sensitivity fall-off at high temporal frequencies is due to early temporal filtering, which should affect equivalent input noise, not calculation efficiency. A limitation of Pelli's study (
1990) was that equivalent input noise was measured at only a few temporal frequencies (0, 4, and 16 Hz), and he did not report sensitivity and calculation efficiency. To test if equivalent input noise is constant at high temporal frequencies, the present study factorized sensitivity into equivalent input noise and calculation efficiency at many temporal frequencies: 0.9375, 1.875, 3.75, 7.5, 15, and 30 Hz.