Our general objective is to measure precisely how color and pattern information are jointly processed in human vision. Detection experiments for a test flash on a large field can isolate various chromatic pathways receiving inputs from different combinations of long (L), middle (M), and short (S) wavelength cones. For stimuli of greater than 520 nm only L and M need be considered. By exciting these in various ratios (positive and negative) we have measured threshold detection contours and have identified 2 separate mechanisms: luminance (Lum) responding to M+L stimulation and red-green chromatic (Chr) responding to the M-L difference. Using the paradigm of the pedestal (coincident in space and time with the test flash), the degree of suprathreshold interaction between these mechanisms is measured. Pedestals of varying strength and different mixture of Lum and Chr components are used. Preliminary results show that for 1 degree test stimuli on a yellow field, Chr detection is weakly facilitated by suprathreshold Lum pedestals and this facilitation persists to very intense pedestals. A kind of suprathreshold independence for Chr detection is thus suggested. Since physiological studies show that in early processing stages (e.g., ganglion cells), spectral tuning is strongly influenced by stimulus size, we will measure the interactions for small-scale stimuli including tests spots down to 5' and sine wave gratings of greater than or equal to 10 cycles/degree. The second thrust of our work is to incorporate S cone excitation. In the 3-dimensional space of S,M, and L stimuli, the threshold is a surface. A minimum of 3 linear mechanisms are required to describe it: presumably, (a) luminance, (b) red-green Chr, and (c) the putative blue-yellow (B-Y) opponent mechanism. If the principle of independence extends to 3-dimensions, the threshold surface will be a parallelepiped. We intend to test this conjecture with precise data. To perform this exacting task we use a computer-controlled 8-channel Maxwellian view system which can deliver positive or negative stimulus increments arbitrarily to the S, L, and M cones. Stimuli can also be given spatial and temporal patterns. By identifying discriminable psychophysical mechanisms, it is possible to identify analogous physiological substrates. These then become anatomical loci whose dysfunction can be discerned noninvasively.

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National Eye Institute (NEI)
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Visual Sciences B Study Section (VISB)
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Harvard University
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Stromeyer 3rd, C F; Martini, P (2003) Human temporal impulse response speeds up with increased stimulus contrast. Vision Res 43:285-98
Stromeyer 3rd, C F (2003) Temporal asymmetry in motion masking: a shortening of the temporal impulse response function. Vision Res 43:261-8
Stromeyer 3rd, C F; Gowdy, P D; Chaparro, A et al. (2000) Colour adaptation modifies the temporal properties of the long- and middle-wave cone signals in the human luminance mechanism. J Physiol 526 Pt 1:177-94
Stromeyer 3rd, C F; Thabet, R; Chaparro, A et al. (1999) Spatial masking does not reveal mechanisms selective to combined luminance and red-green color. Vision Res 39:2099-112
Zemany, L; Stromeyer 3rd, C F; Chaparro, A et al. (1998) Motion detection on flashed, stationary pedestal gratings: evidence for an opponent-motion mechanism. Vision Res 38:795-812
Stromeyer 3rd, C F; Chaparro, A; Rodriguez, C et al. (1998) Short-wave cone signal in the red-green detection mechanism. Vision Res 38:813-26
Stromeyer 3rd, C F; Chaparro, A; Tolias, A S et al. (1997) Colour adaptation modifies the long-wave versus middle-wave cone weights and temporal phases in human luminance (but not red-green) mechanism. J Physiol 499 ( Pt 1):227-54
Chaparro, A; Stromeyer 3rd, C F; Chen, G et al. (1995) Human cones appear to adapt at low light levels: measurements on the red-green detection mechanism. Vision Res 35:3103-18
Picotte, C J; Stromeyer 3rd, C F; Eskew Jr, R T (1994) The foveal color-match-area effect. Vision Res 34:1605-8
Chaparro, A; Stromeyer 3rd, C F; Kronauer, R E et al. (1994) Separable red-green and luminance detectors for small flashes. Vision Res 34:751-62

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