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P Cavanagh

Publications and source records attributed to P Cavanagh.

At least 19 recordsLinked to original sources
PubMed2006

Abnormal spatial selection and tracking in children with amblyopia.

We assessed 18 children with unilateral amblyopia and 30 age-matched controls on one low-level and three high-level motion tasks. Children with amblyopia showed similar performance to controls in both amblyopic and fellow eyes on a low-level global motion task and on a high-level 2-dot apparent motion task. Performance on both single-object and multiple-object attentive tracking tasks was significantly depressed in both amblyopic and fellow eyes relative to controls. These findings suggest that binocular regions of posterior parietal cortex likely contribute to a deficit in voluntary, spatial attention that is a component of amblyopia.

Adolescent↗
PubMed2004

The capacity of visual short-term memory is set both by visual information load and by number of objects.

Previous research has suggested that visual short-term memory has a fixed capacity of about four objects. However, we found that capacity varied substantially across the five stimulus classes we examined, ranging from 1.6 for shaded cubes to 4.4 for colors (estimated using a change detection task). We also estimated the information load per item in each class, using visual search rate. The changes we measured in memory capacity across classes were almost exactly mirrored by changes in the opposite direction in visual search rate (r2=.992 between search rate and the reciprocal of memory capacity). The greater the information load of each item in a stimulus class (as indicated by a slower search rate), the fewer items from that class one can hold in memory. Extrapolating this linear relationship reveals that there is also an upper bound on capacity of approximately four or five objects. Thus, both the visual information load and number of objects impose capacity limits on visual short-term memory.

Adolescent↗
PubMed2001

Unilateral right parietal damage leads to bilateral deficit for high-level motion.

Patients with right parietal damage demonstrate a variety of attentional deficits in their left visual field contralateral to their lesion. We now report that patients with right lesions also show a severe loss in the perception of apparent motion in their "good" right visual field ipsilateral to their lesion. Three tests of attention were conducted, and losses were found only in the contralesional fields for a selective attention and a multiple object tracking task. Losses in apparent motion, however, were bilateral in all cases. The deficit in apparent motion in the parietal patients supports previous claims that this relatively effortless percept is mediated by attention. However, the bilateral deficit suggests that the disruption is due to a bilateral loss in the temporal resolution of attention to transient events that drive the apparent motion percept.

Adult↗
PubMed2001

Attention response functions: characterizing brain areas using fMRI activation during parametric variations of attentional load.

We derived attention response functions for different cortical areas by plotting neural activity (measured by fMRI) as a function of attentional load in a visual tracking task. In many parietal and frontal cortical areas, activation increased with load over the entire range of loads tested, suggesting that these areas are directly involved in attentional processes. However, in other areas (FEF and parietal area 7), strong activation was observed even at the lowest attentional load (compared to a passive baseline using identical stimuli), but little or no additional activation was seen with increasing load. These latter areas appear to play a different role, perhaps supporting task-relevant functions that do not vary with load, such as the suppression of eye movements.

Adult↗
PubMed2001

Visual jitter: evidence for visual-motion-based compensation of retinal slip due to small eye movements.

When dynamic random noise is replaced by static noise after a period of adaptation, adjacent unadapted regions filled with static noise appear to 'jitter' coherently in random directions for several seconds, actually mirroring the observer's own eye movements of fixation [Murakami, I. & Cavanagh, P. (1998). Nature, 395, 798-801]. The present study aims at psychophysically locating two distinct stages underlying this visual jitter phenomenon: a monocular, adaptable stage that measures local retinal motion and a compensation stage that estimates a baseline motion minimum and subtracts it from motion vectors nearby. The first three experiments revealed that visual jitter has storage, directional selectivity, and spatial frequency selectivity, like the motion after-effect does. These results suggest some overlap in the adaptation mechanisms for the two effects, possibly at or below the level of primary visual cortex. The next two experiments revealed the transfer of the effect across the vertical meridian as well as the existence of a preferred stimulus size that is a linear increasing function of eccentricity, mimicking the RF size of the monkey MT neurons. These results suggest that some extrastriate motion area along the parietal pathway including MT mediates motion-based compensation of retinal slip.

Adaptation, Physiological↗
PubMed2001

The spatial resolution of visual attention.

Two tasks were used to evaluate the grain of visual attention, the minimum spacing at which attention can select individual items. First, observers performed a tracking task at many viewing distances. When the display subtended less than 1 degrees in size, tracking was no longer possible even though observers could resolve the items and their motions: The items were visible but could not be individuated one from the other. The limiting size for selection was roughly the same whether tracking one or three targets, suggesting that the resolution limit acts independently of the capacity limit of attention. Second, the closest spacing that still allowed individuation of single items in dense, static displays was examined. This critical spacing was about 50% coarser in the radial direction compared to the tangential direction and was coarser in the upper as opposed to the lower visual field. The results suggest that no more than about 60 items can be arrayed in the central 30 degrees of the visual field while still allowing attentional access to each individually. Our data show that selection has a coarse grain, much coarser than visual resolution. These measures of the resolution of attention are based solely on the selection of location and are not confounded with preattentive feature interactions that may contribute to measures from flanker and crowding tasks. The results suggest that the parietal area is the most likely locus of this selection mechanism and that it acts by pointing to the spatial coordinates (or cortical coordinates) of items of interest rather than by holding a representation of the items themselves.

Adult↗
PubMed2001

Attention-based visual routines: sprites.

A central role of visual attention is to generate object descriptions that are not available from early vision. Simple examples are counting elements in a display or deciding whether a dot is inside or outside a closed contour (Ullman, Cognition 18 (1984) 97). We are interested in the high-level descriptions of dynamic patterns - the motions that characterize familiar objects undergoing stereotypical action - such as a pencil bouncing on a table top, a butterfly in flight, or a closing door. We examine whether the perception of these action patterns is mediated by attention as a high-level animation or 'sprite'. We have studied the discrimination of displays made up of simple, rigidly linked sets of points in motion: either pairs of points in orbiting motion or 11 points in biological motion mimicking human walking. We find that discrimination of even the simplest dynamic patterns demands attention.

Attention↗
PubMed2001

The effect of a geriatric education program on emergency nurses.

OBJECTIVE: In a previous study, emergency nurses gave a high priority to the educational topics of geriatric depression, physical assessment of the elderly, and mental status testing. Our objective was to measure the impact of a 1-day workshop for emergency nurses that addressed these educational needs. METHODS: The workshop consisted of case-based didactic sessions addressing (1) physical assessment of the elderly, (2) delirium, depression, and dementia, and (3) a practical approach to mental status testing in the elderly. The educational program was evaluated using 2 methods: (1) before, and 1 month after, the workshop, participants rated their own practice patterns; and (2) during the course of 2 years, changes in the number of referrals for geriatric assessment and home care from a large emergency department in the study area were monitored. RESULTS: Of 101 ED nurses who attended the 1-day workshop, 51 completed both preworkshop and postworkshop questionnaires (response rate, 50.5%). the most significant self-reported changes in practice 1 month after the workshop were improved screening for depression and altered mental status in older adults (P <.0001 and P <.01, respectively). Other positive changes were noted for inquiring about unplanned weight loss and assistance received at home. A steady increase in the number of referrals for geriatric assessment and home care was noted from the emergency department being monitored. DISCUSSION: Targeted geriatric educational programs can make an impact on the practice of emergency nurses when they are part of an overall, coordinated approach to improving assessment and discharge planning for elderly patients in emergency departments. Mechanisms for reinforcing learning several months after educational events may prove critical to the long-term success of such initiatives.

Aged↗
PubMed2000

Chinese and Americans see opposite apparent motions in a Chinese character.

The perceived direction of apparent motion can be influenced by both "top-down" factors, such as expectation, and by "bottom-up" or stimulus-driven factors, such as grouping (Tse, P., Cavanagh, P. & Nakayama, K. (1998). The role of parsing in high-level motion processing. In T. Watanabe, High-level motion processing - computational, neurobiological and psychophysical perspectives. Cambridge, MA: MIT Press). Here we report the results of a single experiment that pitted top-down cues against bottom-up cues in an apparent motion sequence over the successive strokes of a Chinese character. Although each stroke was in fact presented all at once, subjects raised in China tended to see apparent motion over a single stroke in the direction it would have taken when drawn by hand, even though bottom-up cues drive a percept of apparent motion in the opposite direction for observers unfamiliar with the Chinese language. There is therefore a learned component to motion perception arising from top-down expectations capable of overriding bottom-up cues to motion.

Adult↗
PubMed2000

Limits of attentive tracking reveal temporal properties of attention.

The maximum speed for attentive tracking of targets was measured in three types of (radial) motion displays: ambiguous motion where only attentive tracking produced an impression of direction, apparent motion, and continuous motion. The upper limit for tracking (about 50 deg s-1) was an order of magnitude lower than the maximum speed at which motion can be perceived for some of these stimuli. In all cases but one, the ultimate limit appeared to be one of temporal frequency, 4-8 Hz, not retinal speed or rotation rate. It was argued that this rate reflects the temporal resolution of attention, the maximum rate at which events can be individuated from those that precede or follow them. In one condition, evidence was also found for a speed limit to attentive tracking, a maximum rate at which attention could follow a path around the display.

Attention↗
PubMed2000

Temporal facilitation for moving stimuli is independent of changes in direction.

A flash that is presented aligned with a moving stimulus appears to lag behind the position of the moving stimulus. This flash-lag phenomenon reflects a processing advantage for moving stimuli (Metzger, W. (1932) Psychologische Forschung 16, 176-200; MacKay, D. M. (1958) Nature 181, 507-508; Nijhawan, R. (1994) Nature 370, 256-257; Purushothaman, G., Patel, S.S., Bedell, H.E., & Ogmen, H. (1998) Nature 396, 424; Whitney, D. & Murakami, I. (1998) Nature Neuroscience 1, 656-657). The present study measures the sensitivity of the illusion to unpredictable changes in the direction of motion. A moving stimulus translated upwards and then made a 90 degrees turn leftward or rightward. The flash-lag illusion was measured and it was found that, although the change in direction was unpredictable, the flash was still perceived to lag behind the moving stimulus at all points along the trajectory, a finding that is at odds with the extrapolation hypothesis (Nijhawan, R. (1994) Nature 370, 256-257). The results suggest that there is a shorter latency of the neural response to motion even during unpredictable changes in direction. The latency facilitation therefore appears to be omnidirectional rather than specific to a predictable path of motion (Grzywacz, N. M. & Amthor, F. R. (1993) Journal of Neurophysiology 69, 2188-2199).

Humans↗
PubMed2000

Illusory spatial offset of a flash relative to a moving stimulus is caused by differential latencies for moving and flashed stimuli.

A flash that is presented adjacent to a continuously moving bar is perceived to lag behind the bar. One explanation for this phenomenon is that there is a difference in the persistence of the flash and the bar. Another explanation is that the visual system compensates for the neural delays of processing visual motion information, such as the moving bar, by spatially extrapolating the bar's perceived location forward in space along its expected trajectory. Two experiments demonstrate that neither of these models is tenable. The first experiment masked the flash one video frame after its presentation. The flash was still perceived to lag behind the bar, suggesting that a difference in the persistence of the flash and bar, does not cause the apparent offset. The second experiment employed unpredictable changes in the velocity of the bar including an abrupt reversal, disappearance, acceleration, and deceleration. If the extrapolation model held, the bar would continue to be extrapolated in accordance with its initial velocity until the moment of an abrupt velocity change. The results were inconsistent with this prediction, suggesting that there is little or no spatial compensation for the neural delays of processing moving objects. The results support a new model of temporal facilitation for moving objects whereby the apparent flash lag is due to a latency advantage for moving over flashed stimuli.

Humans↗
PubMed2000

Tracking the apparent location of targets in interpolated motion.

Under appropriate conditions, a target moving in discrete steps can appear to move smoothly and continuously even within the portions of the path where no physical stimulus is present. We investigated the nature of this interpolated motion in attentive tracking displays as well as apparent motion. The results showed that the apparent location of the target moved smoothly through space between the two discrete locations and the judgements of interpolated motion for attentive tracking and apparent motion were comparable to those for continuous motion in both the perceived path and the precision of the judgements. There were few, if any, differences between judgements for real and interpolated motion. An alignment procedure showed that the smooth change in location judgements was real and not a consequence of averaging across discrete locations actually seen on each trial. We also found that the slowest alternation rate which supported accurate location judgements corresponded to a critical SOA of about 500 ms, similar to the longest SOA which supported a subjective impression of motion in the display. Deviations from a constant velocity which were shorter than 200 ms did not register in the judged motion path, suggesting a fairly long time constant for the integration of velocity information into the perceived motion. These results suggest a specialized motion analysis which provides an accurate, explicit model of the interpolated motion path.

Attention↗
PubMed2000

Independent aftereffects of attention and motion.

In the motion aftereffect (MAE), a stationary pattern appears to move in the opposite direction to previously viewed motion. Here we report an MAE that is observed for a putatively high level of visual analysis-attentive tracking. These high-level MAEs, visible on dynamic (but not static) tests, suggest that attentive tracking does not simply enhance low-level motion signals but, rather, acts at a subsequent stage. MAEs from tracking (1) can overrule competing MAEs from adaptation to low-level motion, (2) can be established opposite to low-level MAEs seen on static tests at the same location, and (3), most striking, are specific to the overall direction of object motion, even at nonadapted locations. These distinctive properties suggest MAEs from attentive tracking can serve as valuable probes for understanding the mechanisms of high-level vision and attention.

Attention↗