The nature of the pi1 colour mechanism of W.S. Stiles.

Abstract

SUMMARY1. The Ill colour mechanism was isolated by means of Stiles's auxiliary field technique: that it is H1l which is isolated is proven by both test and field action spectra.2. The fundamental mechanisms of human trichromatic colour vision must satisfy Grassmann's law of additivity. The hypothesis that H., is one of the three fundamentals is tested by experiments in which pairs (Al, /s2) of monochromatic adapting fields are mixed.3. When two fields with wave-lengths in the neighbourhood of its primary mode (JU., #t2 < 500 nm) are combined, HIl is field-additive, consistent with the hypothesis that this portion of the H1 action spectrum is that of the short-wave-length-sensitive photoreceptors.4. When a short-wave-length adaptation field (tl . 500 nm) is mixed with a longer wave-length field (qu2 > 550 nm) H1 is strongly non-additive. This result proves that the long-wave-length portion of the Hl field spectrum is generated at least in part by a signal originating in the long-or middle-wave-length sensitive cones.5. Analysis of the additivity failures supports a model of H, in which the signal to be detected is generated in the short-wave-length cones, and must pass serially through two gain stages: the gain in the first stage is controlled by the short-wave-length cones alone; the gain in the second stage is controlled by a signal originating in the middle, or long-wavelength cones, or both.

Color Vision

“…Shape invariance does hold photons are equal. The most thorough study of field additivity is that of Pugh (1976) who demonstrated that additivity held fo r 'IT! if both p-!…”

Visual sensitivity across the menstrual cycle

“…For the 4.0 log td background, this subject's SWS-cone-mediated sensitivities exhibited additional substantial day-to-day departures from the overall cyclic trend. This adaptation process probably can be identified with the "restoring force" postulated by Pugh and Mollon (1979) to reduce the second-site response polarization in the "yellow" direction caused by the contribution of LWS and0or MWS cone response to an SWS cone spectrally opponent pathway. Recently, Felius and Swanson (2003) showed that thresholds for detecting SWS-cone-mediated response were roughly twice as variable for background stimuli that strongly polarized a spectrally opponent "second site" (Pugh & Mollon, 1979) than for background stimuli that only weakly polarized that site.…”

“…In addition, the ability of the retina to self-regulate its spectrally opponent response appears to differ quantitatively between individuals (Pugh & Mollon, 1979;Shapiro et al, 2003). Several hypothetical reasons were provided in the preceding Discussion, including the role of PMS, and the importance of the retinal locus tested.…”

“…Recently, Felius and Swanson (2003) showed that thresholds for detecting SWS-cone-mediated response were roughly twice as variable for background stimuli that strongly polarized a spectrally opponent "second site" (Pugh & Mollon, 1979) than for background stimuli that only weakly polarized that site. For the 4.0 log td background, this subject's SWS-cone-mediated sensitivities exhibited additional substantial day-to-day departures from the overall cyclic trend.…”

“…Burke, and M.D. In other words, on Day 26, there appeared to be a distinct transition from Stiles' p 1 mechanism to Stiles' p 3 mechanism (Pugh & Mollon, 1979) at about 4.0 log td. The TVI curves for l ϭ 440 nm, l ϭ 540 nm, l ϭ 580 nm, and l ϭ 640 nm are graphed separately in the four panels of Fig.…”