Biomedical subjects

P Atchley

Publications and source records attributed to P Atchley.

17 recordsLinked to original sources

PubMed2001

Spatial attention in early vision.

The present study addressed whether the allocation of attention to a particular region in space can prevent processing of distractor information from non-attended regions. A cue indicated the area in visual space where the target singleton would be presented. Observers were required to detect this target singleton and ignore a distractor singleton presented within a non-attended region. The results indicate that the allocation of attention to a region in space cannot prevent the processing of unwanted information from elsewhere in the visual field. It is concluded that the function of the allocation of attention is not to enhance the processing capacity within the attended region but rather to attenuate interference from distractors in unattended regions.

Adult↗

PubMed2001

The role of attentional breadth in perceptual change detection.

Previous research has shown that changes to scenes are often surprisingly hard to detect. The research reported here investigated the relationship between individual differences in attention and change detection. We did this by assessing participants' breadth of attention in a functional field of view task (FFOV) and relating this measure to the speed with which individuals detected changes in scenes. We also examined how the salience, meaningfulness, and eccentricity of the scene changes affected perceptual change performance. In order to broaden the range of individual differences in attentional breadth, both young and old adults participated in the study. A strong negative relationship was obtained between attentional breadth and the latency with which perceptual changes were detected; observers with broader attentional windows detected changes faster. Salience and eccentricity had large effects on change detection, but meaning aided the performance of young adults only and only when changes also had low salience.

Adolescent↗

PubMed2000

Contingent capture for onsets and offsets: attentional set for perceptual transients.

Four experiments were conducted to examine whether attentional set affects the ability of visual transients (onsets and offsets) to capture attention. In the experiments, visual search for an identity-defined target was conducted. In the first 3 experiments, the target display either onset entirely or was revealed by offsetting camouflaging line segments to reveal letters. Prior to the target display, there was a noninformative cue, either an onset or an offset, at one of the potential target locations. Cues that shared the same transient feature as the target display captured attention. The lack of predictable target transients led to attentional capture by all forms of transients. The final experiments with luminance changes without offsets or onsets showed attentional capture when the luminance changes were large. The results suggest that attentional set can be broadly or narrowly tuned to detect changes in luminance.

Adolescent↗

PubMed2000

Age-related changes in the control of attention in depth.

In 2 experiments, the authors examined the control of spatial attention in depth in advanced age. Observers viewed 2 sets of lines that overlapped in two-dimensional (2-D) space but that were presented at different depth locations. An exogenous cue indicated the depth at which a colored target line would appear. On some trials, a distracting colored element was also presented. The luminance of this distracter varied from high to low. For both older and younger adults, distractors slowed reaction time less if they were at a different depth from the target. This effect was more robust for older adults with low-luminance distractors, indicating an important role for target features as well as attentional control. Adding another feature (i.e., color) that distinguished between target and distracter reduced the effects of slowing shown by the older observers and eliminated the cost of low-luminance distractors for all observers. The results suggest that attentional control in depth is maintained in aging.

Adolescent↗

PubMed2000

Age-related differences in collision detection during deceleration.

Observers were presented with displays simulating a 3-D environment with obstacles in the path of motion. During the trial, observer motion decelerated at a constant rate and was followed by a blackout prior to the end of the display. On some trials the rate of deceleration resulted in stopping before the collision, whereas on other trials the rate of deceleration resulted in a collision with the obstacles. The observer's task was to detect which trials simulated an impending collision. Proportion of collision judgments was greater for older as compared with younger observers when a collision was not simulated. Older observers showed less sensitivity to detect collisions than younger observers did, particularly at high speeds. The age-dependent results are discussed in terms of analyses based on tau and constant deceleration. The results suggest that increased accident rates for older drivers may be due to an inability to detect collisions at high speeds.

Accidents, Traffic↗

PubMed2000

Age-related effects in the marking of old objects in visual search.

Two studies were performed to examine potential age-related differences in visual marking. Visual marking is a limited capacity process that enhances visual search through the inhibition of old objects. In Experiment 1, young and old adults performed three different search conditions: a full-element baseline, a half-element baseline, and a gap condition in which they searched through displays similar to the full-element baseline condition but with half of the letters presented before and the other half of the letters and the target presented after a 1000-ms gap. Both old and young adults displayed search slopes in the gap condition that were equivalent to slopes obtained in the half-element condition, suggesting that they were able to successfully inhibit the old letters. In Experiment 2, old and young adults also performed in three different visual search conditions but in this case with targets defined either by a form difference or by a conjunction of form and color. Both old and young adults showed a reduced slope in the gap as compared to the conjunction condition, suggesting inhibition of the old objects. The data are discussed in terms of age-related differences in the top-down control of attention in visual search.

Adult↗

PubMed1999

Speed, size, and edge-rate information for the detection of collision events.

In the present study an alternative analysis to tau was considered that was based on perceived speed and size and that assumed constant deceleration for the detection of collision events. Observers were presented with displays simulating a 3-D environment with obstacles in the path of observer motion. During the trial, observer motion decelerated at a constant rate and was followed by a blackout prior to the end of the display. Observers had to detect which trials resulted in a collision. The results indicate that collision detection varied as a function of the size of the obstacles, observer speed, and edge rate--findings not predicted by an analysis of tau. The results suggest that observers use an analysis based on speed and size information. A model that assumes constant deceleration is proposed for braking control.

Adult↗

PubMed1999

Attentional effects on preattentive vision: spatial precues affect the detection of simple features.

Most accounts of visual perception hold that the detection of primitive features occurs preattentively, in parallel across the visual field. Evidence that preattentive vision operates without attentional limitations comes from visual search tasks in which the detection of the presence of absence of a primitive feature is independent of the number of stimuli in a display. If the detection of primitive features occurs preattentively, in parallel and without capacity limitations, then it should not matter where attention is located in the visual field. The present study shows that even though the detection of a red element in an array of gray elements occurred in parallel without capacity limitations, the allocation of attention did have a large effect on search performance. If attention was directed to a particular region of the display and the target feature was presented elsewhere, response latencies increased. Results indicate that the classic view of preattentive vision requires revision.

Adolescent↗

PubMed1999

The discrimination of heading from optic flow is not retinally invariant.

Three experiments were conducted to determine whether the discrimination of heading from optic flow is retinally invariant and to determine the importance of acuity in accounting for heading eccentricity effects. In the first experiment, observers were presented with radial flow fields simulating forward translation through a three-dimensional volume of dots. The flow fields subtended 10 degrees of visual angle and were presented at 0 degree, 10 degrees, 20 degrees, and 40 degrees of retinal eccentricity. The observers were asked to indicate whether the simulated movement was to the right or the left of a target that appeared at the end of the display sequence. Eye movements were monitored with an electrooculogram apparatus. In a second experiment, static acuity thresholds were derived for each of the observers at the same retinal eccentricities. There was a significant increase in heading detection thresholds with retinal eccentricity (from 0.92 degree at 0 degree retinal eccentricity to 3.47 degrees at 40 degrees). An analysis of covariance indicated that the variation in sensitivity to radial flow, as a function of retinal eccentricity, is independent of acuity. Similar results were obtained when the Vernier acuity of observers was measured. These results suggest that the discrimination of heading from radial flow is not retinally invariant.

Adult↗

PubMed1998

Hemispheric specialization in the detection of subjective objects.

Three experiments were conducted to examine hemispheric specialization for the detection of subjective objects. In the first two experiments, observers searched for the presence of a square defined by subjective contours. The first experiment demonstrated that the left hemisphere made more errors for detecting these objects. The second experiment showed that the increased errors were due to the left hemisphere responding to the individual features of the objects and not the objects as a whole. In the second experiment, the right hemisphere was also faster for detecting the absence of a subjective object. A third experiment was conducted to determine if performance for the right hemisphere was due to object level processing. It was shown that the right hemisphere only makes illusory conjunctions for features within perceptual groups while the left hemisphere makes illusory conjunctions both within and across perceptual groups, providing converging evidence for object level processing in the right hemisphere. The results suggest that the right hemisphere conjoins feature information for the perception of objects.

Adult↗

PubMed1998

Attentional control within 3-D space.

Four experiments investigated whether directing attention to a particular plane in depth enables observers to filter out information from another depth plane. Observers viewed stereoscopic displays and searched for a red line segment among green line segments. The results showed that directing attention to a particular depth plane cannot prevent attentional capture from another depth plane when the colors of the target and distractor are identical. However, it can prevent attentional capture by a singleton from another depth plane when the colors of the target and distractor are different. These results indicate that only when both color and depth information are selective in guiding attention to the target singleton can attentional capture by irrelevant singletons be prevented. The results also suggest that retinal disparity does not have the same special status as location information in two dimensions and should be considered as just another feature along which selection may occur.

Adolescent↗

PubMed1998

The effect of age, retinal eccentricity, and speed on the detection of optic flow components.

Forty observers participated in a study examining the effect of age on the detection of motion in central and peripheral vision. Detection of lamellar (Experiment 1) and radial flow (Experiment 2) was measured for 20 younger observers and 20 older observers (10 men and 10 women in each group). Motion thresholds were measured for angles of 0 degree, 10 degrees, 20 degrees, and 40 degrees off fovea. The results indicated significant differences between older and younger adults for both motion types. The effect of age was mediated by the gender of the observer as well as the retinal eccentricity of the display. Older women showed higher thresholds for lamellar flow at fovea, consistent with previous findings. The findings suggest that age-related changes in visual information processing are affected by changes in the temporal characteristics of the motion processing system. A model is proposed in which 2 different streams of processing are used for the recovery and use of motion information.

Adult↗

PubMed1998

Spatial cuing in a stereoscopic display: attention remains "depth-aware" with age.

Previous research has demonstrated that spatial attention is "depth-aware": Reaction times (RT) are greater for shifts in depth and two-dimensional (2-D) space than in 2-D space alone. This experiment examined whether the ability to focus attention at a depth location is maintained with advanced age. Twelve younger and 12 older observers viewed stereoscopic displays in which one of four spatial locations was cued. Two of the locations were at a near depth location and two were at a far depth location. When the focus of visual attention was shifted to a new location in space (because of an invalid cue), the cost in RT for switching attention (measured as the difference between RT on valid cue and invalid cue trials) was greater when observers had to switch attention between different depth locations and different locations in 2-D space than for shifts in 2-D space alone. This effect was observed for both younger and older observers, suggesting that the ability to orient attention to a depth location is maintained with age.

Adolescent↗

PubMed1998

Cooperativity, priming, and 3-D surface detection from optic flow.

Three experiments were conducted to determine whether the mechanisms responsible for the detection of three-dimensional (3-D) surfaces from optic flow operate in a cooperative manner. The first experiment was conducted to determine whether a hysteresis effect occurs for 3-D surface detection from optic flow. The results of the first experiment demonstrated a hysteresis effect with lower thresholds occurring for decreasing texture density than for increasing texture density. The second experiment used a priming methodology to determine whether this form of cooperativity was based on preactivation of shear detectors or preactivation of 2-D motion detectors. The results suggest that only shear detectors were primed. The third experiment utilized a similar methodology to determine whether a surface representation would produce a priming effect. We found no evidence that the priming effect found in the second experiment was the result of preactivation of a generic representation of the test stimuli. The results of the experiments, considered together, suggest priming of the mechanisms responsible for recovering shear.

Humans↗

PubMed1997

Smoothness of the velocity field and three-dimensional surface detection from optic flow.

Five experiments were conducted to determine the importance of smoothness of the velocity field in detecting 3-D surfaces from optic flow. Subjects were presented with optic flow displays simulating either points positioned on a corrugated 3-D surface or points randomly positioned within a 3-D volume. The subject's task was to indicate whether or not the display appeared to be a 3-D surface. Smoothness of the velocity field was examined by systematically varying the speed of individual velocities in the flow field according to a Gaussian distribution with M = 0 and SD = sigma. Variations in frequency, amplitude, density, and surface complexity were also examined. Detection of the corrugated surfaces systematically declined with an increase in sigma. An increase in frequency of the corrugation for simple (single-frequency corrugation) surfaces resulted in a decrease in surface detection accuracy. Accuracy increased with an increase in density and amplitude for both simple and complex (multiple-frequency corrugation) surfaces. An analysis of the deformation of the displays predicted performance on the basis of human observers, providing further support for the importance of deformation for 3-D surface detection.

Depth Perception↗

PubMed1995

Discrimination of speed distributions: sensitivity to statistical properties.

Two experiments examining the ability of human observers to detect differences in the statistical properties underlying velocity distributions were conducted. A four-alternative forced-choice methodology, using four simultaneous velocity distributions, was used in both experiments. In the first experiment the value of one statistical moment (mean, variance, skewness, or kurtosis) was manipulated while the others were held constant. The subjects task was to determine which of four velocity distributions contained the dissimilar value. In the second experiment only the latter three moments were examined. A similar procedure was used, however feedback was given after each trial to maximize observer performance. The results from both experiments indicate that human observers can reliably detect differences in both mean and variance information underlying velocity distributions. The results of this research has important implications for image segmentation and the detection of heading from optic flow.

Discrimination, Psychological↗

PubMed1995

Age-related differences in the detection of three-dimensional surfaces from optic flow.

The present study examined age-related differences in sensitivity to optic flow for the detection of 3-D surfaces. Observers were presented with optic flow displays simulating either a 3-D corrugated surface or a random velocity pattern and were asked to detect the 3-D corrugated surface display. Performance decrements were found for older (mean age = 71) compared with younger (mean age = 21) observers across variations in density and corrugation frequency. Older observers also showed performance decrements for a motion coherence task, but performance on this task was not significantly correlated with performance on the 3-D surface detection task. These results suggest that performance on 2-D motion tasks is not necessarily predictive of performance on complex 3-D motion tasks. In addition, the results suggest that different processes underlie the analysis of 2-D and 3-D motion.

Adult↗