Effect of the short-wavelength-sensitive-cone mosaic and rods on the locus of unique green.

A primary goal of this study was to establish whether the magnitude of the short-wavelength-sensitive- (S-) cone signal into the yellow/blue (Y/B) mechanism was influenced by the absolute or the relative numbers of S cones. This was assessed by measuring the locus of unique green for various test sizes at four eccentric locations chosen to exploit differences in the underlying mosaic of S cones. In general, the locus of unique green was unaffected by test size, retinal quadrant, or rod input but was influenced by retinal eccentricity. The locus of unique green shifted to shorter wavelengths as retinal eccentricity increased from 1 degrees to 8 degrees. The data do not support a model whereby the S-cone signal is determined by the absolute number of S cones, but a model based on the relative number of S cones cannot be eliminated.

Spatial summation in human cone mechanisms from 0 degrees to 20 degrees in the superior retina.

The maximum area of complete spatial summation (i.e., Ricco's area) for human short-wavelength-sensitive-(S-) and long-wavelength-sensitive- (L-) cone mechanisms was measured psychophysically at the fovea and at 1.5 degrees , 4 degrees , 8 degrees , and 20 degrees along the vertical meridian in the superior retina. Increment thresholds were measured for three observers by a temporal two-alternative forced-choice procedure. Test stimuli ranging from -0.36 to 4.61 log area (min2) were presented on concentric 12.3 degrees adapting and auxiliary fields, which isolated either an S- or an L-cone mechanism on the plateau of its respective threshold versus intensity function. Test flash durations were 50 and 10 ms for the S- and L-cone mechanisms, respectively. The data indicate that, from 0 degrees to 20 degrees, Ricco's area increases monotonically for the L-cone mechanism, is variable for the S-cone mechanism, and is larger for the S-cone mechanism than for the L-cone mechanism for essentially all retinal locations. This pattern of results most likely reflects differences in ganglion cell density and changes in neural convergence with retinal eccentricity.

Effect of the S-cone mosaic and rods on red/green equilibria.

The loci of unique blue and unique yellow were measured with and without a rod bleach for various test sizes in the fovea and at 1 and 8 deg nasal and superior retinal eccentricities. Test sizes and retinal positions were selected to systematically manipulate the absolute and relative numbers of S cones underlying the test stimuli. The results revealed the following: (1) The locus of unique blue shifted to longer wavelengths as the absolute number of S cones underlying the test stimulus increased, suggesting that the S-cone neural weighting factor of the red/green (R/G) opponent model is linked to the absolute number of S cones. (2) In general, the locus of unique yellow remained invariant, although changes were observed in the superior retina. This finding indicates that either the L-to-M-cone ratio may not be invariant across all retinal quadrants or that this ratio may not determine the locus of unique yellow. (3) Rod signals affected the locus of the unique hues, especially at small test sizes, demonstrating an influence of rods on the R/G opponent mechanism.

The bimodality of unique green revisited.

Unique green measurements were obtained from 50 females and 50 males under eight different experimental conditions. Combinations of two different test sizes (0.25 and 1.0 deg) and four different background fields (none, 62.5, 250, and 1000 td) comprised the experimental conditions under which unique green measurements were made. Group and gender frequency distributions of the unique green loci were examined for the eight experimental conditions. Differences in the shape of the frequency distributions were noted for the different test sizes and backgrounds as well as for gender, but none of the experimental parameters appeared to elicit a statistically significant bimodal distribution.

Unique hue judgments as a function of test size in the fovea and at 20-deg temporal eccentricity.

Unique hue loci were measured for four observers in the fovea and at 20-deg temporal eccentricity as a function of test size. Eccentric measurements were made on the cone plateau following a rod bleach. The results indicate that unique yellow remains approximately invariant with respect to test size and retinal eccentricity, whereas unique blue and unique green shift to longer wavelengths with increasing test size. The locus of unique blue in the periphery reaches an asymptote at approximately the same wavelength as that from the foveal measurements, whereas unique green measured in the periphery is consistently at shorter wavelengths than in the fovea. In general, the data are best described by a model in which the short-wavelength-sensitive cone input to the two opponent-color channels decreases with decreasing test size and increasing retinal eccentricity.

Spectral efficiency measured by heterochromatic flicker photometry is similar in human infants and adults.

Spectral efficiency functions based on heterochromatic flicker photometry (HFP) were measured for three adults and 42 infants using a rapid visually-evoked potential (VEP) method. A 5 degrees-diameter, broadband standard (0.6 cd/m2) was presented in square-wave counterphase (15 Hz) with one of 13 monochromatic lights (420-660 nm; 20 nm steps). The intensity of the monochromatic light was continuously varied while extracting the phase-locked VEP amplitude of the fundamental component. HFP functions measured psychophysically by the method of adjustment were also obtained for the adults. Adult HFP functions from the two methods were found to be essentially the same. Both of these functions were compared to Vos'-modified 2 degrees V(lambda) function and the 10 degrees CIEV(lambda) function. The mean adult data were slightly better fit to the 2 degrees V(lambda) function than to the 10 degrees CIEV(lambda) function, although there was an elevation in sensitivity at 420 and 440 nm. Infant HFP functions were similar to Vos' modified V(lambda) except for an elevation in efficiency at short wavelengths. The mean infant HFP function agreed better with the 10 degrees CIEV(lambda) function than Vos'-modified V(lambda) function, but infant sensitivity was elevated by 0.4 log units at 420 nm compared to the 10 degrees CIE observer. The elevation found at short wavelengths for both adults and infants is attributed to individual and age-related variation in the density of the ocular media, and to reduced macular pigment screening resulting from use of a 5 degrees field size.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetic short-wavelength sensitivity: variations with induced changes in blood glucose level.

PURPOSE: To investigate variations in diabetic short-wavelength sensitivity with acute, induced changes in blood glucose level. METHODS: Increment threshold measures were obtained for short-wavelength-sensitive and middle/long-wavelength-sensitive cone pathways after an induced, acute change in blood glucose level in diabetic observers. RESULTS: Diabetic observers showed an increase in short-wavelength sensitivity, but no change in middle/long-wavelength sensitivity, with a rapid drop in blood glucose level. CONCLUSIONS: Experimentally induced changes in diabetic blood glucose levels can directly affect diabetic short-wavelength sensitivity.

LWS cone effects on rod threshold and saturation in achromats with residual cone function.

Rod saturation on flashed and steady red backgrounds was investigated in normals and three achromats, two of whom were found to have some residual cone function. LWS cones selectively reduce the background level at which rod saturation occurs and elevate rod thresholds at flashed background levels well below saturation. Both of these LWS cone actions are also present in eyes with greatly reduced LWS cone function. In normal eyes LWS cones also elevate rod thresholds on steady backgrounds. We thus conclude that LWS cones influence rods through different mechanisms under transient (flashed) and steady-state background stimulation and that the increase in rod visual sensitivity observed during prolonged presentation of a background is due to a time-dependent reduction of LWS cone influence on rods. Finally, the finding that rod-cone interactions of the same magnitude found in normals can be seen in individuals where the cones' ability to mediate vision is severely reduced suggests the rod saturation paradigm as a sensitive technique for revealing residual LWS cone function.

Additivity of spatially induced blackness.

Tests of additivity of the postreceptoral pathways that mediate the perception of blackness were conducted under conditions of spatial contrast. Observers increased the radiance of a surrounding annulus until a broadband (white) test center appeared completely black. Additivity tests with heterochromatic flicker photometry (HFP) and direct brightness matching were also conducted for each observer. The results indicated that the luminance level of the annulus required to induce blackness did not change with variations in spectral composition. Results consistent with additivity were also obtained for HFP, but the results from brightness matching were not consistent with additivity. The data support the view that the perception of blackness is mediated by neural mechanisms that additively combine the input of middle- and long-wave photoreceptors.

Estimating middle-wavelength and long-wavelength cone sensitivity with large, long-duration targets and small, brief targets.

Incremental threshold versus field-intensity curves (tvi) and spectral sensitivity functions were measured for 500 nm and 667 nm test flashes, either under the standard two-colour threshold conditions of Stiles (target: 1.0 deg, 200 ms)--which are known to favour detection by the chromatically-opponent pathways--or with a smaller (0.1 deg), shorter-duration (10 ms) target--chosen to favour detection by the non-opponent (achromatic) pathway. The data reveal differences between the two conditions: for the small, brief target, the tvi curves were shallower and less dependent upon wavelength, and the spectral sensitivity functions were narrower than for the standard target.

Temporal induction of blackness--I. Color appearance.

Three color-normal observers described the appearance of colors under conditions of temporal induction. One of four inducing fields (unique blue, unique green, unique yellow, unique white) was foveally viewed for 5 sec followed immediately by a 400 msec reference stimulus of the same size (0.75 deg) and spatial location as the inducing field. The reference stimulus was 3 or 5 td and appeared achromatic to the observer when viewed without the inducing field. After presentation of this temporal sequence, the observers described the reference stimulus by assigning percentages to the terms red, green, yellow, blue, white and black. The range of inducing field intensities was -0.4-3.2 log td. Both chromatic and achromatic induction occurred at low illuminance levels of the inducing fields. As the illuminance of the inducing field increased, the reference stimulus gradually became blacker and the chromatic components less prominent. The minimum illuminance level at which the reference appeared 100% black was the same for the four different inducing fields.

Temporal induction of blackness--II. Spectral efficiency and tests of additivity.

The perception of blackness was investigated by measuring spectral efficiency and field additivity under conditions of temporal induction. For both purposes, observers foveally viewed a 0.75 deg, inducing stimulus for 5 sec followed immediately (or 200 msec later) by a broadband (5500 K) reference stimulus of the same size and spatial location. For spectral efficiency measurements, the inducing field was a monochromatic light between 400 and 700 nm (10 nm steps), while the additivity studies involved various wavelength mixtures. The psychophysical task was to increase the radiance of the inducing field until the reference stimulus just turned completely black. For two observers the spectral efficiency function of temporally-induced blackness more closely resembled their heterochromatic flicker photometry (HFP) function than their direct brightness-matching function. Their brightness functions were characterized by an inflection at about 580 nm which is generally ascribed to subtractive cone interactions, but their blackness-induction and HFP functions did not show this inflection. The brightness function of the third observer did not show an inflection at 580 nm, thereby making it difficult to differentiate between her three spectral efficiency functions. Overall, the subtle differences between the various spectral efficiency functions made it difficult to determine whether blackness induction was more similar to HFP or brightness matching. The results from the additivity tests of blackness induction, HFP and direct brightness matching removed this ambiguity from the spectral efficiency findings. Blackness induction and HFP were shown to be additive, whereas the results from brightness matching showed clear additivity failures of the cancellation type. These data support the view that the perception of blackness is mediated by neural mechanisms that additively combine the inputs of middle- and long-wave photoreceptors.

Isolation of short-wavelength-sensitive cone photoreceptors in 4-6-week-old human infants.

Spectral sensitivity was measured for nine infants, 4-6 weeks of age, and three adults under conditions of chromatic adaptation chosen to reveal the presence of short-wavelength-sensitive cones. Monochromatic test stimuli (400-550 nm) were presented at 2 Hz superimposed on a broadband, yellow background. Following 4 min of adaptation to the background, test stimuli were presented while recording the steady-state, visually-evoked cortical potential (VECP). Response averages were obtained for several radiance levels at each test wavelength, and the amplitude of the fundamental frequency was extracted from the digitized response with a fast-Fourier transform. These data were used to construct response vs intensity functions for each wavelength. A fixed criterion response was chosen from the latter family of functions to generate individual spectral sensitivity curves. These VECP spectral sensitivity functions matched the psychophysically-determined functions of adults, measured by the method of adjustment and with the same stimulus configuration. Peak sensitivity for infants and adults under these conditions occurred at about 440 nm, and the main lobe of the curve (400-500 nm) was well fitted by the Vos-Walraven short-wavelength cone fundamental. The only major difference between the infant and adult data was in the relative sensitivity of the secondary mode of the curves (above 500 nm). These results demonstrate the presence of short-wavelength-sensitive cones and a functional pathway to the visual cortex by 4-6 weeks of age.

Perception of blackness.

We sought to measure the mechanisms underlying the perception of blackness in the following way. A central spot (45') of fixed luminance was surrounded by a dark ring (7.5'), and surrounding all was an annular zone (30') of light. This stimulus was presented in Maxwellian view for 0.5 sec every 3 sec. The radiance of the annulus required to make the central area (spot and ring) appear uniformly black was measured for different wavelengths (440-660 nm) of the annulus. These measurements were made for test spots that were either broadband or of wavelength 480, 500, 580, or 660 nm. In all conditions the measured spectral efficiency of induced blackness matched the inverse of the V lambda function. Using the same stimulus, we have also measured increment-threshold functions. For a fixed luminance of the spot, the radiance of the surrounding annulus required to bring the central spot to threshold was measured. These increment-threshold functions do not match the V lambda or blackness functions. Our results show that induced blackness is inversely related to the luminous efficiency function and that the spectral efficiency of induced blackness is distinct from the increment-threshold function measured under these conditions. Furthermore, blackness appears to be independent of the wavelengths of the inducing annulus as well as of the central spot. Thus these results link induced blackness to the luminance pathway and argue against the involvement of the chromatic pathways in the perception of blackness.

Early development of aggression in chickens: The relative importance of pecking and leaping.

A longitudinal study (employing a multiple separation technique) of chicks' social behavior over the first postnatal month indicated systematic changes in their mode of physical interactions. During the first week or so, intersubject pecking in same-sex pairs was frequent, and was more likely in birds with a home cage advantage (i.e., a prior resident effect). However, there were no sex differences in any of the forms of social pecking (head, body, or feet of the opponent), and all types showed significant decreases over the period of the study. On the contrary, there was a strong effect for sex on rates of aggressive leaping, with males exhibiting more leaps than females. Further, there was a clear increase in leaping over the first weeks of testing, and something of a decline thereafter. These data suggest that in this species the definitive expression of aggressive or dominance behavior may be leaping. Early social pecking (during a period in which this behavior was at its maximum rate) did not predict the subsequent leaping behavior of individuals, but later "leap orders" were highly associated with later "peck orders".