Paul Atchley

Conversation limits the functional field of view

The purpose of these two experiments is to investigate one possible mechanism that might account for an increase in crash risk with in-car phone use: a reduction in the functional field of view. In two between-subjects experiments, college undergraduates performed a task designed to measure the functional field of view in isolation and while performing a hands-free conversational task. In both experiments, the addition of the conversational task led to large reductions in the functional field of view. Because similar reductions have been shown to increase crash risk, reductions in the functional field of view by conversation may be an important mechanism involved in increased risk for crashes with in-car phone use. Actual or potential applications of this research include improving driver performance.

VISUAL MARKING OF OLD OBJECTS

Watson and Humphreys (1997) presented evidence that selection of new elements can be prioritized by on-line top-down attentional inhibition of old stimuli already in the visual field (visual marking). The experiments on which this evidence was based always presented old elements in green and new elements in blue. Because of this, instead of prioritizing new objects by inhibiting old objects, selection could have been based on color. The present experiment, which does not contain this confound, showed that visual marking is a strong and robust process that enables subjects to visually mark at least 15 old elements even when these elements have the same color as the new elements. The results indicate that preview of the elements is critical—not the fact that those elements contained a common feature.

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.

Spatial cuing in a stereoscopic display: Evidence for a "depth-aware" attentional focus

Two experiments were conducted to explore whether attentional selection occurs in depth, or whether attentional focus is “depth blind,” as suggested by Ghiradelli and Folk (1996). In Experiment 1, 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, and a single target was presented along with three distractors. The results indicated a larger cost in reaction time for switching attention inx,y and depth than inx,y alone, supporting a “depth-aware” attentional spotlight. In Experiment 2, no distractors were present, similar to the displays used by Ghiradelli and Folk. In this experiment, no effect for switching attention in depth was found, indicating that the selectivity of attention in depth depends on the perceptual load imposed on observers by the tasks and displays.

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.

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 observers 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.

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.

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.

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° of visual angle and were presented at 0°, 10°, 20°, and 40° 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° at 0° retinal eccentricity to 3.47° at 40°). 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.

Attentional control in 3-D space

Two experiments investigated the nature of attention in 3-D space. In Experiment 1, the hypothesis that attention can be localized to a depth plane was tested. Observers searched for a red line in two arrays of green lines. The arrays of lines were near in 2-D space but separated in depth. Search for the target was faster when the depth plane where the target would appear was cued, indicating attention can be localized in depth. A second experiment tested the hypothesis that attending to a location in depth would reduce the effect of a distracter at other depth locations. In this experiment, search for a tilted red line was faster when a distracting vertical line was present at another depth than when it was present at the same depth as the target. Implications for display design using depth information is discussed.