Todd Macuda

Further evidence for hierarchical chunking in rat spatial memory.

In Experiment 1, rats were given a test to determine the order of preference among 3 types of food. Two groups of rats then were trained on a 12-arm radial maze in Experiment 2, with the 3 foods placed in fixed-arm locations for 1 group and in locations that varied randomly across sessions for the other group. The results replicated those of Dallal and Meck (1990) by showing faster learning and more clustering of arm choices by food type in the fixed-locations group than in the random-locations group. Two further experiments were performed to test the chunking hypothesis. Observations of working memory in Experiment 3 and the reorganization of reference memory in Experiment 4 both supported the chunking hypothesis by showing superior spatial memory and arm chunking by food type when chunk integrity was maintained than when it was compromised.

Memory for number of light flashes in the pigeon

Two groups of pigeons were trained to perform symbolic delayed matching-to-sample at a 0-sec delay with sample stimuli that consisted of sequences of light flashes. The sequences varied in number but not time for one group (number group) and in time but not number for the other group (time group). When retention was tested at delays up to 10 sec in Experiment 1, a choose-small effect was found in the number group, and a choose-long effect was found in the time group. Transfer tests between number and time samples in Experiment 2 supported the hypothesis that pigeons were discriminating between the number of light flashes at the end of sample sequences in Experiment 1. It was concluded that pigeons in both the number and the time groups were discriminating between number of flashes and that the apparent choose-long effect was actually a choose-small effect. The implications of these findings for the mode-control model of counting and timing (Meck & Church, 1983) were discussed.

Luminance and chromatic discrimination in the horse (Equus caballus)

Equine colour vision was measured under conditions that minimised the possibility of animals using brightness cues to make chromatic discriminations. In a two-stage study, we first obtained luminance discrimination functions for achromatic targets then tested for chromatic discrimination over a range of target luminances. Horses were trained on a two-choice discrimination task. The positive stimulus was varied in luminance and/or colour using neutral density and broad band colour filters. The negative stimulus appeared as a uniform grey. In the brightness discrimination task, the horses performed well at large luminance differences but their percentage of correct responses declined to near chance levels at differences of less than 0.2 log units. In addition, a decrement in performance was noted at luminance differences of less than 0.2 log units for green and yellow chromatic discrimination functions, suggesting that horses cannot easily discriminate yellow and green from grey. However, the chromatic discrimination functions for red and blue showed that animals performed very well across the full range of target luminances. These results suggest that horses are at least dichromats.

The Retinal Ganglion Cell Layer and Visual Acuity of the Camel

We examined the retinal ganglion cell layer of the dromedary camel, Camelus dromedarius. We have estimated that there are 8 million neurons in the ganglion cell layer of this large retina (mean area of 2,300 mm–2). However, only approximately 1 million are considered to be ganglion cells. The ganglion cells are arranged as two areas of high cell density, one in the temporal and one in the nasal retina. Densities of ganglion cells between these two high density regions is much lower, often less than 100 per mm–2. In between these two high density regions, on the nasal side of the optic nerve head, is a unique and dense vertical streak of mostly non-ganglion cells; the function of this specialization is unknown. On the basis of ganglion cell density we estimate that the peak acuity in the dromedary camel is about 10 and 9.5 cycles per degree in the temporal and nasal high density regions respectively and falls to 2–3 cycles per degree in the central retina. Behavioral acuity was estimated for one bactrian camel and was found to be approximately 10 cyc deg–1. The camel has a retina with a mean thickness of 104 µm, less than the 143 µm thickness that has previously been thought to be necessary for a retinal vasculature. Nevertheless, there is an extensive vitreal vasculature that does not appear to spare any retinal region.

Detection of motion-defined form under simulated night vision conditions

The influence of Night Vision Goggle-produced noise on the perception of motion-defined form was investigated using synthetic imagery and standard psychophysical procedures. Synthetic image sequences incorporating synthetic noise were generated using a software model developed by our research group. This model is based on the physical properties of the Aviator Night Vision Imaging System (ANVIS-9) image intensification tube. The image sequences either depicted a target that moved at a different speed than the background, or only depicted the background. For each trial, subjects were shown a pair of image sequences and required to indicate which sequence contained the target stimulus. We tested subjects at a series of target speeds at several realistic noise levels resulting from varying simulated illumination. The results showed that subjects had increased difficulty detecting the target with increased noise levels, particularly at slower target speeds. This study suggests that the capacity to detect motion-defined form is degraded at low levels of illumination. Our findings are consistent with anecdotal reports of impaired motion perception in NVGs. Perception of motion-defined form is important in operational tasks such as search and rescue and camouflage breaking. These degradations in performance should be considered in operational planning.

The Impact of Night Vision Goggles on Way-Finding Performance and the Acquisition of Spatial Knowledge

Objective: This study examined the effects of night vision goggles (NVGs) on navigation and way-finding performance and the acquisition of spatial knowledge. Background: Although numerous studies have examined the effects of NVGs on visual perception, few have examined the effects of using NVGs on the acquisition and expression of spatial cognition. Method: Participants learned the environment through active navigation and way finding, searching for targets within a life-sized maze with or without NVGs. Knowledge of the environment was then tested with two spatial memory tests. Results: Findings show that navigation and way finding with NVGs appear to be harder, as indicated by longer navigation times and additional, unnecessary turns, than they are without NVGs. Moreover, change in navigation performance over the course of the way-finding trials varied as a function of group assignment indicating that NVGs influenced the learning process. NVG users demonstrated a significant decrease in navigation times earlier as well as significant decreases in navigational legs compared with the control group. In judging the positions of objects relative to target objects in different rooms in the maze, performance was better for participants without NVGs than for those with NVGs. In a map-drawing task, participants in the NVG group were more likely to position objects incorrectly and to receive worse scores than the controls. Conclusion: These results demonstrate that NVGs affected not only spatial navigation and way-finding performance but also the acquisition of spatial knowledge. Application: These degradations in spatial knowledge should be considered in operational planning and NVG training programs.

Detection of motion-defined form using night vision goggles

Perception of motion-defined form is important in operational tasks such as search and rescue and camouflage breaking. Previously, we used synthetic Aviator Night Vision Imaging System (ANVIS-9) imagery to demonstrate that the capacity to detect motion-defined form was degraded at low levels of illumination (see Macuda et al., 2004; Thomas et al., 2004). To validate our simulated NVG results, the current study evaluated observer’s ability to detect motion-defined form through a real ANVIS-9 system. The image sequences consisted of a target (square) that moved at a different speed than the background, or only depicted the moving background. For each trial, subjects were shown a pair of image sequences and required to indicate which sequence contained the target stimulus. Mean illumination and hence image noise level was varied by means of Neutral Density (ND) filters placed in front of the NVG objectives. At each noise level, we tested subjects at a series of target speeds. With both real and simulated NVG imagery, subjects had increased difficulty detecting the target with increased noise levels, at both slower and higher target speeds. These degradations in performance should be considered in operational planning. Further research is necessary to expand our understanding of the impact of NVG-produced noise on visual mechanisms.

Intraocular transfer and simultaneous processing of stimuli presented in different visual fields of the pigeon.

Differences in neuroanatomy, optics, and function indicate the operation of 2 visual systems in pigeons, a frontal field system and a lateral field system. Communication between these systems was examined with a delayed matching-to-sample task in which sample stimuli could be presented in either the frontal or lateral fields. In Experiment 1, matching acquired with the lateral field transferred to the frontal field but did not transfer from the frontal field to the lateral field. When different samples were presented simultaneously to the frontal and lateral fields in Experiment 2, pigeons preferred to match the sample in the frontal field, but lateral field information interfered to some extent with frontal field matching. The 3rd experiment showed left lateral field dominance when the left and right fields were simultaneously presented with different sample stimuli; left field dominance was not complete, as pigeons sometimes matched the right-field sample.

Comparison of Three Night Vision Intensification Tube Technologies on Resolution Acuity: Results from Grating and Hoffman ANV-126 Tasks

Several methodologies have been used to determine resolution acuity through Night Vision Goggles. The present study compared NVG acuity estimates derived from the Hoffman ANV-126 and a standard psychophysical grating acuity task. For the grating acuity task, observers were required to discriminate between horizontal and vertical gratings according to a method of constant stimuli. Psychometric functions were generated from the performance data, and acuity thresholds were interpolated at a performance level of 70% correct. Acuity estimates were established at three different illumination levels (0.06-5X10-4 lux) for both procedures. These estimates were then converted to an equivalent Snellen value. The data indicate that grating acuity estimates were consistently better (i.e. lower scores) than acuity measures obtained from the Hoffman ANV-126. Furthermore significant differences in estimated acuity were observed using different tube technologies. In keeping with previous acuity investigations, although the Hoffman ANV-126 provides a rapid operational assessment of tube acuity, it is suggested that more rigorous psychophysical procedures such as the grating task described here be used to assess the real behavioural resolution of tube technologies.

Night Vision Goggle External Lighting Effects

The National Research Council of Canada, Transport Canada and the Federal Aviation Administration examined external lighting and night vision goggle interaction by quantifying the effects of incompatible lighting on visual acuity and recording pilot comments. Four observers and three sets of lights were tested using Landolt ring visual acuity charts created for distances of 15.2, 30.5 and 45.7 m. NVG compatible external lights provided consistent acuity scores in a symmetrically lit visual field. Acuity scores varied greatly with incompatible lights that caused an asymmetric viewing field. Implications for civil NVG operations are discussed.