Most diurnal Neotropical primates have polymorphic color vision that can result in multiple types of dichromats and trichromats living in the same social group. We have modeled how well these genotypes would be predicted to distinguish dietary fruits from the visual background of leaf tops and leaf bottoms as a classification problem implemented by support vector machines (SVMs). We measured reflectance spectra of fruits and leaves, and irradiance spectra of incident light to compute quantum catches of genetically diverse cones of three sympatric primates in Amazonian Ecuador. We constructed MacLeod-Boynton chromaticity spaces for each genotype and trained SVMs to classify fruits and leaves based on color, then added a third dimension for luminance. For metrics of performance, we used classification accuracy and also the area under ROC curves (AUC), which allowed calculation of 95% confidence intervals (CIs, range 0-1). In the absence of luminance information, in direct sunlight trichromats are predicted to distinguish fruit from leaf tops with accuracies of 91-96% compared to 59-73% for dichromats; CIs of the AUCs do not overlap. When luminance was incorporated, predicted performance of trichromats did not improve, but predicted accuracy for dichromats increased to 71-79%; some CIs overlapped slightly with trichromats. For the more common (and more difficult) discrimination of fruit vs leaf bottoms, predicted accuracy based on color decreased to 76-92% for trichromats and 64-71% for dichromats; CIs had small amounts of overlap that varied among genotypes. Adding luminance information had little effect on predicted accuracy for trichromats (76%-88%), but increased predicted accuracy for dichromats to 66%-82%; now CIs of dichromats overlapped extensively with those of trichromats. Thus, dichromats may be able to use luminance information to minimize the potential advantage that trichromats have in a critical foraging discrimination. More detailed comparisons among types of trichromats and dichromats will also be presented.

Psychophysics is a hybrid field of science encompassing study of the perceptual responses of subjects to sensory stimuli that are carefully controlled and measured by the methods of physics. A nutrition-related feature of the retina that can be assessed by psychophysics is the density of the carotenoid pigments lutein and zeaxanthin that accumulate in the central depression called the fovea. Age-related cataracts develop slowly over a lifetime and epidemiologic studies that focus only on patients with well-established cataracts may miss factors important in the early development of cataract. The psychophysical detection task is explained using suprathreshold stimuli, and then the subject is given 30-40 minutes of dark adaptation. The macular pigment (MP) is an accumulation of the two carotenoids lutein and zeaxanthin in the fovea and in the immediately surrounding retina. Most etiologic studies of these conditions, however, have focused on patients that already exhibit frank clinical symptoms.

Abstract A recent focus in community ecology has been on how within‐species variability shapes interspecific niche partitioning. Primate color vision offers a rich system in which to explore this issue. Most neotropical primates exhibit intraspecific variation in color vision due to allelic variation at the middle‐to‐long‐wavelength opsin gene on the X chromosome. Studies of opsin polymorphisms have typically sampled primates from different sites, limiting the ability to relate this genetic diversity to niche partitioning. We surveyed genetic variation in color vision of five primate species, belonging to all three families of the primate infraorder Platyrrhini, found in the Yasuní Biosphere Reserve in Ecuador. The frugivorous spider monkeys and woolly monkeys (Ateles belzebuth and Lagothrix lagotricha poeppigii, family Atelidae) each had two opsin alleles, and more than 75% of individuals carried the longest‐wavelength (553–556 nm) allele. Among the other species, Saimiri sciureus macrodon (family Cebidae) and Pithecia aequatorialis (family Pitheciidae) had three alleles, while Plecturocebus discolor (family Pitheciidae) had four alleles—the largest number yet identified in a wild population of titi monkeys. For all three non‐atelid species, the middle‐wavelength (545 nm) allele was the most common. Overall, we identified genetic evidence of fourteen different visual phenotypes—seven types of dichromats and seven trichromats—among the five sympatric taxa. The differences we found suggest that interspecific competition among primates may influence intraspecific frequencies of opsin alleles. The diversity we describe invites detailed study of foraging behavior of different vision phenotypes to learn how they may contribute to niche partitioning.

We examined photic and ecological factors related to initiation of feeding by four sympatric primates in the rain forest of Amazonian Ecuador. With rare exceptions, morning activities of all taxa began only after the onset of nautical twilight, which occurred 47-48 min before sunrise. The larger spider and woolly monkeys, Ateles belzebuth and Lagothrix lagotricha poeppigii, left their sleeping trees before sunrise about half the time, while the smaller sakis and titi monkeys, Pithecia aequatorialis and Plecturocebus (formerly Callicebus) discolor, did not emerge until sunrise or later. None of the four taxa routinely began feeding before sunrise. Pithecia began feeding a median 2.17 h after sunrise, at least 0.8 h later than the median feeding times of the other three taxa. The early movement of Ateles and Lagothrix, and late initiation of feeding by Pithecia are consistent with temporal niche partitioning. Among most New World primate species, all males and many females, have dichromatic color vision, with only two cone photopigments, while some females are trichromats with three cone photopigments. Current evidence indicates that the dichromats have a foraging advantage in dim light, which could facilitate utilization of twilight periods and contribute to temporal niche partitioning. However, in our study, dichromatic males did not differentially exploit the dim light of twilight, and times of first feeding bouts of female Ateles and Lagothrix were similar to those of males. First feeding bouts followed a seasonal pattern, occurring latest in May-August, when ripe fruit abundance and ambient temperature were both relatively low. The most frugivorous taxon, Ateles, exhibited the greatest seasonality, initiating feeding 1.4 h later in May-August than in January-April. This pattern may imply a strategy of conserving energy when ripe fruit is scarcer, but starting earlier to compete successfully when fruit is more abundant. Lower temperatures were associated with later feeding of Ateles (by 26 min / °C) and perhaps Pithecia, but not Lagothrix or Plecturocebus. The potential for modification of temporal activity patterns and temporal niche partitioning by relatively small changes in temperature should be considered when predicting the effects of climate change.

Vision is one of the principal senses of primates. It plays such a dominant role that the morphology of the visual apparatus is one criterion for distinguishing primates from other mammalian forms. Classical tests of color vision include sensitivity to light of different wavelengths, ability to distinguish differences between two similar wavelengths, and ability to distinguish a faintly colored light from an achromatic, white light. In absorption spectrophotometry, spectra can be plotted on a logarithmic scale and slid vertically for comparison, as is done in the bottom panel. The distinctive characteristics of the reflectance spectra encouraged to compare plant specimens of similar colors to determine whether their reflectance spectra could be categorized in some parsimonious way. The size of the fruit influences both the probability of seed dispersal and the fruit's spectral appearance. Other things being equal, large objects appear more saturated in color than small ones and hence will be more conspicuous.

Among New World primates, only one genus out of 18 is known to have routine trichromatic color vision like humans. All other species investigated to date have diverse color vision genotypes that suggest potential diversity in their visual ecology. Some evidence indicates that specific color vision phenotypes, particularly dichromats, are more successful when foraging in dim light or foraging for cryptic prey. Using light spectra measured during the transition from darkness to daylight, and behavioral data collected during ongoing studies, we analyzed the timing of the earliest activities requiring vision. For four sympatric primates at the Tiputini Biodiversity Station in Amazonian Ecuador we found no evidence of activity occurring before the onset of nautical twilight (~48 min before sunrise). Observers on the ground frequently thought that monkeys began their morning activity in darkness, but measures of the quantum flux between 400 and 700 nm showed that only 1-2% of the light at canopy level reaches the ground, so the light available to the animals is ~2 log units higher. The larger monkeys (Ateles and Lagothrix), whose diets include a high proportion of ripe fruit, left their sleeping trees and began to move through the canopy earlier than the smaller monkeys whose diets are more diverse (Callicebus) or include more cryptic, unripe fruits (Pithecia). Although human observers at canopy level were able to distinguish colors and fine detail at 21-23 min before sunrise, most of the monkeys waited until after sunrise to begin feeding. For the larger monkeys, 80-90% of the feeding bouts occurred after sunrise, and for the smaller monkeys, 100% of the feeding bouts occurred after sunrise. Thus, it appears that the monkeys wait for good viewing conditions before feeding, and they are not exploiting the dim light of twilight where dichromacy might confer some advantages. Meeting abstract presented at VSS 2017

Intersaccadic periods of fixation are characterized by incessant retinal motion due to small eye movements. While these movements are often disregarded as noise, the temporal modulations they introduce to retinal receptors are significant. However, analysis of these input modulations is challenging because the intersaccadic eye motion is close to the resolution limits of most eyetrackers, including widespread pupil-based video systems. Here, we analyzed in depth the limits of two high-precision eyetrackers, the Dual-Purkinje Image and the scleral search coil, and compared the intersaccadic eye movements of humans to those of a non-human primate. By means of a model eye we determined that the resolution of both techniques is sufficient to reliably measure intersaccadic ocular activity up to approximately 80Hz. Our results show that the characteristics of ocular drift are remarkably similar in the two species; a clear deviation from a scale-invariant spectrum occurs in the range between 50 and 100Hz, generally attributed to ocular tremor, leading to intersaccadic retinal speeds as high as 1.5deg/s. The amplitude of this deviation differs on the two axes of motion. In addition to our experimental observations, we suggest basic guidelines to evaluate the performance of eyetrackers and to optimize experimental conditions for the measurement of ocular drift and tremor.

For a behavioral neuroscientist, fixational eye movements are a double-edged sword. On one edge, they make control of visual stimuli difficult, but on the other edge they provide insight into the ways the visual system acquires information from the environment. We have studied macaque monkeys as models for human visual systems. Fixational eye movements of monkeys are similar to those of humans but they are more often vertically biased and spatially more dispersed. Eye movements scatter stimuli from their intended retinal locations, increase variability of neuronal responses, inflate estimates of receptive field size, and decrease measures of response amplitude. They also bias against successful stimulation of extremely selective cells. Compensating for eye movements reduced these errors and revealed a fine-grained motion pathway from V1 feeding the cortical ventral stream. Compensation is a useful tool for the experimenter, but rather than compensating for eye movements, the brain utilizes them as part of its input. The saccades and drifts that occur during fixation selectively activate different types of V1 neurons. Cells that prefer slower speeds respond during the drift periods with maintained discharges and tend to have smaller receptive fields that are selective for sign of contrast. They are well suited to code small details of the image and to enable our fine detailed vision. Cells that prefer higher speeds fire transient bursts of spikes when the receptive field leaves, crosses, or lands on a stimulus, but only the most transient ones (about one-third of our sample) failed to respond during drifts. Voluntary and fixational saccades had very similar effects, including the presence of a biphasic extraretinal modulation that interacted with stimulus-driven responses. Saccades evoke synchronous bursts that can enhance visibility but these bursts may also participate in the visual masking that contributes to saccadic suppression. Study of the small eye movements of fixation may illuminate some of the big problems in vision.

PURPOSE:Unhealthy lifestyles have been associated with increased odds for age-related macular degeneration (AMD). Whether this association is modified by genetic risk for AMD is unknown and was investigated.DESIGN:Interactions between healthy lifestyles AMD risk genotypes were studied in relation to the prevalence of AMD, assessed 6 years later.PARTICIPANTS:Women 50 to 79 years of age in the Carotenoids in Age-Related Eye Disease Study with exposure and AMD data (n=1663).METHODS:Healthy lifestyle scores (0-6 points) were assigned based on Healthy Eating Index scores, physical activity (metabolic equivalent of task hours/week), and smoking pack years assessed in 1994 and 1998. Genetic risk was based on Y402H in complement factor H (CFH) and A69S in age-related maculopathy susceptibility locus 2 (ARMS2). Additive and multiplicative interactions in odds ratios were assessed using the synergy index and a multiplicative interaction term, respectively.MAIN OUTCOME MEASURES:AMD presence and severity were assessed from grading of stereoscopic fundus photographs taken in 2001-2004. AMD was present in 337 women, 91% of whom had early AMD.RESULTS:The odds of AMD were 3.3 times greater (95% confidence interval [CI], 1.8-6.1) in women with both low healthy lifestyle score (0-2) and high-risk CFH genotype (CC), relative to those who had low genetic risk (TT) and high healthy lifestyle scores (4-6). There were no significant additive (synergy index [SI], 1.08; 95% CI, 0.70-1.67) or multiplicative (Pinteraction=0.94) interactions in the full sample. However, when limiting the sample to women with stable diets before AMD assessment (n=728) the odds for AMD associated with low healthy lifestyle scores and high-risk CFH genotype were strengthened (odds ratio, 4.6; 95% CI, 1.8-11.6) and the synergy index was significant (SI, 1.34; 95% CI, 1.05-1.70). Adjusting for dietary lutein and zeaxanthin attenuated, and therefore partially explained, the joint association. There were no significant additive or multiplicative interactions for ARMS2 and lifestyle score.CONCLUSIONS:Having unhealthy lifestyles and 2 CFH risk alleles increased AMD risk (primarily in the early stages), in an or additive or greater (synergistic) manner. However, unhealthy lifestyles increased AMD risk regardless of AMD risk genotype.

During natural vision, we scan scenes of a world full of colors with large and small eye movements. Surprisingly, the responses of cortical neurons are seldom studied under these conditions. Most commonly, gray scale images are displayed, and eye movements are mimicked by movie sequences that assume the eye is stationary during intersaccadic intervals. The results indicate that cortical activity is very low and sparse when viewing achromatic movies. We have recorded activity of V1 neurons while a monkey viewed calibrated color images of natural scenes from the McGill database and performed eye movement tasks. Eye position was recorded at high precision with a scleral search coil so that fixational saccades, drifts, and tremor were measureable. There was a wide range of response characteristics, but many neurons were continuously active during drift periods as well as immediately after saccades. This activity would be expected to contribute to the fine detailed vision that is enabled by fixational drift. However, it poses a challenge to determine whether the drift-related activity integrates easily into the rubric of sparse coding. When saccades were performed from a blank field to a natural image or vice-versa, we were able to separate the situations where the receptive field lands on a region of a natural scene or leaves it. We are currently investigating the balance of “on” and “off” responses that accompany these abrupt changes. Many of the neurons gave quite vigorous responses to colored images that were often greater than the response to the same image converted to gray scale. This comparison offers a novel measure of the contribution of color to cortical activity and the metabolic cost of this important perceptual capacity. Meeting abstract presented at VSS 2015