Chromatic suppression of cone inputs to the luminance flicker mechanism

SUMMARY1. Human short-wave S cone signals are important for colour vision and here we examine whether the S cone signals also contribute to motion and luminance.2. Detection was measured with moving patterns that selectively stimulated S cones -violet sine-wave gratings of 1 cycle deg-' on an intense yellowish field. For rates up to 12 Hz, detection was governed by non-directional mechanisms, possibly of a chromatic nature, as shown by three findings: moving gratings had to be suprathreshold for their direction to be identified; the threshold ratio of counterphase flickering versus moving gratings was low; and direction-selective adaptation was essentially absent. 3. Evidence for less sensitive, directional mechanisms includes the following: at high velocity, the direction of movement of the violet gratings can be identified just slightly above the detection threshold; directional adaptation was strong with a suprathreshold test pattern; velocity was seen veridically for clearly suprathreshold patterns; and a counterphase flickering test, added in spatial-temporal quadrature phase to a similar suprathreshold mask, had identical detection and directionidentification thresholds.4. Interactions of long-wave L cone and S cone signals in direction-selective mechanisms were measured with an orange counterphase grating and a violet counterphase test, both flickering at the same rate and presented in spatial quadrature phase on the yellowish adapting field. Direction identification thresholds, measured as a function of the temporal phase of two gratings, demonstrated both that the S cone signal lags considerably behind the L cone signal (an effect that strongly varies with S cone light adaptation), and more strikingly, the S cone signal summates with a negative sign and thus is effectively inverted in direction-selective mechanisms.5. Quantitatively similar temporal phase functions were obtained with uniform violet and orange flicker when a luminance discrimination criterion was used: thus the S cone signal summates negatively with the L cone signal for both discrimination of luminance flicker and the direction of motion.6. The temporal phase functions accurately predicted threshold summation for * To whom correspondence should be sent. J. LEE AND C. F. STROMEYER IIIidentifying the direction of motion of a pair of violet and orange gratings moving with the same velocity but with different spatial phase offsets. Once the relative temporal phase lag of the S cones was compensated for, there was linear threshold summation for the violet and orange patterns when presented in effective (physiological) spatial antiphase, and clear cancellation when presented in phase. This and related experiments show a linear summation of S, M and L cone signals for direction detection, with the S cones having a negative sign. The luminance contrast sensitivity is very high for the spectrally long-wave member of the pair of gratings (300-500 at 8 Hz), suggesting that the patterns are detected with high-contrastsensitivity mechanisms such as ...

Section: S Cone Input To Luminance Mechanismssupporting

confidence: 49%

Section: S Cone Input To Luminance Mechanismsmentioning

confidence: 99%

Contribution of human short‐wave cones to luminance and motion detection.

Lee

Stromeyer

1989

“…1B). The luminance mechanism (Stromeyer et al 1987) responds to a weighted sum of L and M cone-contrast, laL' + bMl, with coefficients a and b of the same sign, implying a negative slope (Fig. 1B).…”

Section: Moving Gratings: Detection and Direction Identificationmentioning

confidence: 99%

Contributions of human long‐wave and middle‐wave cones to motion detection.

Stromeyer

Kronauer

Ryu

et al. 1995

“…Swanson, Pokorny & Smith (1988) observed that, at intermediate temporal frequencies (6 Hz), orange adapting backgrounds induced a considerable phase lag of the L' signal relative to M'; the phase shift weakly reversed on green backgrounds. Measurements at higher frequencies (15 Hz) showed that coloured backgrounds also influence the relative L' and M' weights (Eisner & MacLeod, 1981;Stromeyer et al 1987). Orange backgrounds selectively suppressed the L' contrast signal (more than Weberian cone-selective adaptation predicts) while green backgrounds selectively suppressed the M' contrast signal.…”

mentioning

confidence: 99%

“…The LUM mechanism is best revealed using rapid flicker or motion. The LUM mechanism responds to a weighted sum of L' and M, but the relative contrast weights may vary considerably with adapting field colour (Eisner & MacLeod, 1981;Stromeyer, Cole & Kronauer, 1987). Lesions of the phasic, magnocellular (MC) pathway strongly elevate contrast thresholds for detecting rapid flicker or motion (Schiller et al 1990;Merigan, Byrne & Maunsell, 1991).…”

mentioning

confidence: 99%

Colour adaptation modifies the long‐wave versus middle‐wave cone weights and temporal phases in human luminance (but not red‐green) mechanism.

Stromeyer¹,

Chaparro²,

Tolias³

et al. 1997

1. The human luminance (LUM) mechanism detects rapid flicker and motion, responding to a linear sum of contrast signals, L' and M', from the long-wave (L) and middle-wave (M) cones. The red-green mechanism detects hue variations, responding to a linear difference of L' and M' contrast signals. 2. The two detection mechanisms were isolated to assess how chromatic adaptation affects summation of L' and M' signals in each mechanism. On coloured background (from blue to red), we measured, as a function of temporal frequency, both the relative temporal phase of the L' and M' signals producing optimal summation and the relative L' and M' contrast weights of the signals (at the optimal phase for summation). 3. Within the red-green mechanism at 6 Hz, the phase shift between the L' and M' signals was negligible on each coloured field, and the L' and M' contrast weights were equal and of opposite sign. 4. Relative phase shifts between the L' and M' signals in the LUM mechanism were markedly affected by adapting field colour. For stimuli of 1 cycle deg' and 9 Hz, the temporal phase shift was zero on a green-yellow field (-570 nm). On an orange field, the L' signal lagged M' by as much as 70 deg phase while on a green field M' lagged L' by as much as 70 deg. The asymmetric phase shift about yellow adaptation reveals a spectrally opponent process which controls the phase shift. The phase shift occurs at an early site, for colour adaptation of the other eye had no effect, and the phase shift measured monocularly was identical for flicker and motion, thus occurring before the motion signal is extracted (this requires an extra delay). 5. The L' versus M' phase shift in the LUM mechanism was generally greatest at intermediate temporal frequencies (4)(5)(6)(7)(8)(9)(10)(11)(12) and was small at high frequencies (20-25 Hz). The phase shift was greatest at low spatial frequencies and strongly reduced at high spatial frequencies (5 cycle deg-'),indicating that the receptive field surround of neurones is important for the phase shift. 6. These temporal phase shifts were confirmed by measuring motion contrast thresholds for drifting L cone and M cone gratings summed in different spatial phases. Owing to the large phase shifts on green or orange fields, the L and M components were detected about equally well by the LUM mechanism (at 1 cycle deg-' and 9 Hz) when summed spatially in phase or in antiphase. Antiphase summation is typically thought to produce an equiluminant red-green grating. 7. At low spatial frequency, the relative L' and M' contrast weights in the LUM mechanism (assessed at the optimal phase for summation) changed strongly with field colour and temporal frequency. (-20ims) relative to the centre.