The recognition and representation of edge blur: Evidence for spatial primitives in human vision

Experiments are reported that measure the precision with which observers can (a) discern the degree of blur of an edge, (b) distinguish between two different types of blur, and relate the locations of two such edges by judging their (c) misalignment or (d) separation. Three blurring functions were used, and detailed examination of the retinal stimulus in each case leads to a simple hypothesis for the visual coding of edge blur. This is interpreted in terms of a general and primitive code for the transduction of local and widespread spatial luminance changes, in which stationary points in an approximation to the second derivative are detected and localized. The phenomena of illusory brightness changes in Mach bands and the Chevreul illusion find a ready explanation in this theory.     

Visible persistence: Effects of luminance, spatial frequency and orientation

Square-wave gratings of various space-average luminances, spatial frequencies and orientations were presented briefly to observers, who were asked to adjust a brief visual probe to coincide with the end of the longer-lasting, gradually decaying sensory trace of these stimuli. Visible persistence of 2 and 7 c/deg gratings increased with increasing luminance, and an interaction was found at approx. 6 cd/m2 between luminance and spatial frequency. The persistence curves showed a low-pass frequency characteristic at low mean luminance levels, whereas at high luminances, they presented a band-pass frequency characteristic. Persistence of a 7 c/deg grating was longer at oblique orientations than at horizontal or vertical orientations. These findings were related to properties of transient and sustained channels in human vision.     

Spatiotemporal contrast sensitivity and visual field locus

Contrast sensitivity, measured as a function of retinal eccentricity for stimuli differing in temporal and spatial frequency (0.25-9 c/deg; 0-16 Hz, 0-12 degrees eccentricity), was maximum at the fovea and declined linearly with eccentricity. The slope of the decrease depended upon spatial but not temporal frequency. Contrast sensitivity for drifting gratings was approximately twice that for sinusoidal counterphase gratings at all eccentricities. For central viewing log contrast sensitivity increased with grating length. The shape of this function was systematically related to spatial frequency but independent of temporal frequency, indicating that the visual field is homogeneous in sensitivity for change in contrast over time. The implications of these findings for mechanisms of threshold vision in fovea and periphery are discussed.     

Local Ecological Factors, Ultrafine Particulate Concentrations, and Asthma Prevalence Rates in Buffalo, New York, Neighborhoods

Previous to this study various healthcare utilization studies and house-to-house surveys had shown that Buffalo's west side had a high utilization rate for asthma and high asthma prevalence in comparison with neighboring communities. The relative contributions of traffic-related pollution and personal and local ecological factors to the high asthma rates were still unknown. To investigate the potential roles of personal home environmental factors and local ecological factors in variations of asthma prevalence in Buffalo neighborhoods, we conducted a cross-sectional survey of a systematic random sample of 2000 households in the city of Buffalo, New York, with a response rate of 80.4%. We found that the odds of having at least one person with asthma per household on Buffalo's west side was 2.57 times [95% confidence interval (CI) = 1.85-3.57] that of Buffalo's east side. There were no statistically significant differences in the odds of finding at least one person with asthma in households of other Buffalo neighborhoods. We further found no difference in the odds of having asthma on Buffalo's west side even after correcting for race/ethnicity, household triggers of asthma, and socioeconomic factors. Monitoring ultrafine particulates showed increased levels in communities downwind of the Peace Bridge Complex and major roadways supplying it. A multiple-regression model showed that asthma prevalence may be influenced by humidity and ultrafine particulate concentrations. These results suggest that increased asthma risk may be influenced by chronic exposure to personal and local ecological factors.     

Converging cerebellofugal inputs to the thalamus

Summary The extent of thalamic projections from punctate sites in the cerebellar nuclei was examined in 22 acutely prepared cats by mapping monosynaptic field potentials evoked in the ventrolateral (VL) nucleus by stimulation of the interpositus and dentate nuclei (IN and DN). The monosynaptic field potentials were evoked in the VL by low current stimulating pulses applied at high frequency to these cerebellar nuclei. Quantification of the projections was possible since the conditions of stimulation and recording were strictly controlled. The incoming volley recorded in the brachium conjunctivum caudally to the VL was also analysed. It was composed of two amplitude peaks with different latencies, corresponding to two groups of fibres conducting at 60–90 m/s and 20–25 m/s respectively. The negative field potentials in VL also showed two amplitude peaks and different latencies. The differences in latency between the first and second peaks in the presynaptic and postsynaptic field potentials are compatible with the possibility that both groups of afferent fibres may be monosynaptically connected to VL relay cells. The cerebello-thalamic projections were mapped and their density gradient was established. Two or three small thalamic strips of dense projections surrounded by a large zone of weaker projections were observed to emerge from each punctate cerebellar site. In the discussion of the functional significance of these findings, it is suggested that this organization might constitute a modulatable morphological support for a mechanism focalizing the cerebello-cortical inputs.     

Hippocampal function and behavior: spatial discrimination and response inhibition

Rats were tested preoperatively and following fimbria-fornix lesions in a spatial memory task on a radial arm maze. With a free choice procedure, fimbria-fornix lesions produced both changes in response patterns and a deficit in spatial discrimination. With a confinement procedure which interrupted the response tendencies seen in the free choice procedure, fimbria-fornix lesions did not produce perseverative response patterns but did produce a failure of spatial discrimination. These results demonstrate that fimbria-fornix lesions alter both motor response patterns and spatial discrimination, but that the two effects occur independently.     

Effects of dose and period of neonatal alcohol exposure on the context preexposure facilitation effect

Background: Alcohol exposure in the rat on postnatal days (PD) 4 to 9 is known to partially damage the hippocampus and to impair hippocampus‐dependent behavioral tasks. We previously reported that PD4 to 9 alcohol exposure eliminated the context preexposure facilitation effect (CPFE) in juvenile rats, a hippocampus‐dependent variant of contextual fear conditioning. In the CPFE, context exposure and immediate shock occur on successive occasions and this produces conditioned freezing relative to a control group that is not preexposed to the training context. Here, we extend our earlier findings by examining the effects of neonatal alcohol administered at multiple doses or over different neonatal exposure periods. Method: Rat pups (male and female) were exposed to a single binge dose of alcohol at one of 3 doses (2.75, 4.00, or 5.25 g/kg/d) over PD4 to 9 (Experiment 1) or to 5.25 g over PD4 to 6 or PD7 to 9 (Experiment 2). Sham‐intubated (SI) and undisturbed (UD) rats served as controls. On PD31, rats were preexposed to either the training context (Pre) or an alternate context (No‐Pre). On PD32, rats received an immediate unsignaled footshock (1.5 mA, 2 seconds) in the training context. Finally, on PD33, all rats were returned to the training context and tested for contextual freezing over a 5‐minute period. Results: Undisturbed‐ and SI‐Pre rats showed the CPFE, i.e., context preexposure facilitated contextual conditioning, relative to their No‐Pre counterparts. The immediate shock deficit was present in all No‐Pre groups, regardless of previous alcohol exposure. In Experiment 1, blood alcohol level was negatively correlated with contextual freezing. Group 2.75 g‐Pre did not differ from controls. Group 4.00 g‐Pre froze significantly less than Groups UD‐ and SI‐Pre but more than Group 5.25‐Pre, which showed the immediate shock deficit. In Experiment 2, alcohol exposure limited to PD7 to 9, but not PD4 to 6, disrupted the CPFE. Conclusions: This is the first demonstration of dose‐related impairment on a hippocampus‐dependent task produced by neonatal alcohol exposure in the rat. Exposure period effects support previous studies of alcohol and spatial learning. The CPFE is a more sensitive behavioral task that can be used to elucidate developmental alcohol‐induced deficits over a range of alcohol doses that are more relevant to human exposure levels.