We investigated the spatio-temporal frequency selectivity properties of 248 neurons in VI and VII of the macaque monkey, and the receptive field properties of 43 inferotemporal neurons of the owl monkey. The study of VI and VII neurons was carried out using sine wave gratings. Our results show that VI and VII neurons were selective to different but partially overlapping spatial frequency ranges (at retinal eccentricities of 2°-5°, VII neurons are tuned approximately two octaves lower than VI neurons). The spatial frequency bandwidths for the two visual areas are similar. The temporal frequency selectivity of VI neurons was mostly lowpass (70%), or wide bandpass (30%, mean bandwidth 3 octaves); 62% of VII neurons had bandpass temporal frequency tuning curves (mean bandwidth 2 octaves). The range of preferred temporal frequencies and the bandwidths of VII neurons suggest the existence of at least two non-overlapping temporal frequency filters at each spatial frequency. Results also indicate that spatial and temporal selectivities are independent fundamental properties. Our results may provide physiological support for psychophysical findings in man, suggesting several independent detection mechanisms centered at different temporal frequencies, especially at low spatial frequencies. In a different study, a possible substructure of the large inferotemporal receptive fields was investigated in the owl monkey. A novel kind of stimulus derived from the Gabor elementary functions was used as test signal. A first set of stimuli with a constant relative spatial frequency bandwidth was used to probe the existence of either one or more than one spatial frequency band within one receptive field. A second set of constant spatial width was used to test the neruon's spatial frequency selectivity. Results suggest that only one orientation and spatial frequency band project onto each neuron. The preferred spatial frequencies (0.2 - 0.6 c/deg) were in the very low spatial frequency range for this animal. The spatial frequency bandwidth comparable to that of striate cells, the inclusion of many cycles of the preferred spatial frequency within the receptive field, and the generally reduced response to constant aperture test signals, suggest non-linear processing during summation of information from preceding visual areas.

The overall goals of this dissertation were 1) to understand the role that neurons in primate primary visual cortex (V1) play in the detection of small visual stimuli, and 2) to understand the quantitative relationship between the responses of individual neurons and neural population responses in V1. These goals were addressed in experiments with awake, behaving macaque monkeys using electrophysiological and imaging techniques. Initially, I employed ideal observer models to assess V1 neural detection sensitivity in a reaction-time visual detection task and found it to be comparable to the monkey's detection sensitivity. Using the same detection task, I found weak, but significant, correlations between V1 neural activity and the trial-by-trial behavior of monkeys (choice and reaction time). The conclusion of these studies is that the monkey's behavior in the detection task was likely mediated by large neural populations. Voltage-sensitive dye imaging (VSDI) is a powerful imaging technique that is well suited for assessing the link between the activity of large neural populations and behavior. VSDI measures changes in membrane potential over a cortical area of 1-2 cm² with high spatial and temporal resolutions. Using position tuning experiments with VSDI and electrophysiology, I described the relatively unknown quantitative relationships between spiking activity, the local field potential, and VSDI. These relationships were well captured by non-linear transfer functions. Lastly, these experiments also revealed important new findings about the representation of visual space by populations of neurons in V1. In particular, we resolved a long standing debate regarding the size of the cortical point image (CPI), the area of cortex activated by a single point stimulus. We found that the CPI is constant across eccentricity in parafoveal V1, suggesting that each point in space activates an approximately equivalent amount of cortical tissue. In conclusion, the results and analyses described in this dissertation contribute to our understanding of the role that neural populations in V1 play in mediating visual detection, reveal important properties of the representation of visual space by populations of neurons in V1, and provide the first analysis of the quantitative relationship between VSDI and electrophysiological signals. / text

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In light of exceptionally delayed reproductive senescence exhibited by a 64 year old female chimpanzee (Pan troglodytes) housed in Florida, endocrinal analyses meant to determine the state of her current reproductive viability were conducted. Urine was collected from the study subject for a period of 88 days spaced within an interim of roughly 6 months and the specimens were sent to the Hominoid Reproductive Ecology Laboratory for assessment. Additional data was collected from three control females in order to provide a basis of comparison against the hormonal markers present in the geriatric study animal. Results indicate that the geriatric female does not presently appear to be cycling, but nor does she exhibit signs of complete reproductive cessation. This could signify that Pan troglodytes adheres to a pattern of reproductive aging not necessarily shared by Homo sapiens, which has further implications for the evolutionary trajectory of menopause in the human female. / by Christina T. Cloutier. / Thesis (M.A.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.