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Paul A Warren

Publications and source records attributed to Paul A Warren.

6 recordsLinked to original sources
PubMed2006

The pop out of scene-relative object movement against retinal motion due to self-movement.

An object that moves is spotted almost effortlessly; it "pops out". When the observer is stationary, a moving object is uniquely identified by retinal motion. This is not so when the observer is also moving; as the eye travels through space all scene objects change position relative to the eye producing a complicated field of retinal motion. Without the unique identifier of retinal motion an object moving relative to the scene should be difficult to locate. Using a search task, we investigated this proposition. Computer-rendered objects were moved and transformed in a manner consistent with movement of the observer. Despite the complex pattern of retinal motion, objects moving relative to the scene were found to pop out. We suggest the brain uses its sensitivity to optic flow to "stabilise" the scene, allowing the scene-relative movement of an object to be identified.

Attention↗
PubMed2005

Explicit estimation of visual uncertainty in human motion processing.

We examine whether human observers have explicit access to an estimate of their own uncertainty in extrapolating the motion trajectories of moving objects. Objects moved across a display area at constant speed changing direction at short time intervals. Each new direction was obtained by adding a random perturbation to the previous direction. The perturbation distribution was always symmetric with mean zero (no change in direction) but could differ in variability: objects with low directional variability tended to travel in straight lines while objects with high directional variability moved more erratically. Objects eventually disappeared behind the near edge of an occluder. Observers marked a 'capture region' along the far edge of the occluder that they estimated would contain the object when it re-emerged. We varied both occluder width and directional variability across trials and found that observers correctly compensated for these changes. We present a two-stage model of observer performance in which the visual system first estimates the directional variability of the object and then uses this estimate to set a capture region.

Cues↗
PubMed2004

Consistency of Listing's law and reciprocal innervation with pseudo-inverse control of eye position in 3-D.

Pseudo-inverse kinematics, under which small movements are produced by the least possible sum square changes in motor command, has been proposed as a unifying principle for the elimination of redundancy in general biological motor control systems (Pellionsz 1984) and in particular in the oculomotor system (Daunicht 1988, 1991). We have noted elsewhere (Dean et al, 1999) that this principle is incomplete without first specifying a parameterisation of motor command space and we proposed that the relevant motor-command parameter is summed motor unit firing rate. Under this assumption we were able to show that pseudo-inverse control of the horizontal extraocular muscles is consistent with available motor pool firing rate data. In this paper we extend this result to three dimensions and six extraocular muscles, showing that pseudo-inverse control is consistent with published firing rate date for a realistic model of oculomotor kinematics. We suggest that pseudo-inverse control may represent a common currency for modular control of many degree of freedom systems while its implementation may be a consequences of the minimisation of a more ecologically relevant parameter such as post-saccadic retinal slip.

Biomechanical Phenomena↗
PubMed2004

Interpolating sampled contours in 3D: perturbation analyses.

In four experiments, observers interpolated parabolic sampled contours confined to planes in three-dimensional space. Each sampled contour consisted of eight visible points, placed irregularly along the otherwise invisible parabolic contour. Observers adjusted an additional point until it fell on the contour. We sought to determine how each visible point influenced interpolation by measuring the effect of slightly perturbing its location. Influence fell rapidly to zero as distance from the interpolated point increased, indicating that human visual interpolation of parabolic contours is local. We compare the measured influence for human observers to that predicted by three standard interpolation algorithms. The results were inconsistent with a fit of a quadratic to the points, but were reasonably consistent with a cubic spline and most consistent with an algorithm that minimizes the variance of angles between neighboring line segments defined by the sampled points.

Algorithms↗
PubMed2002

Interpolating sampled contours in 3-D: analyses of variability and bias.

In two experiments, we examined how observers interpolated the missing parts of sampled, planar contours in 3-D space. We varied (1) contour type (linear or parabolic), (2) orientation of the plane containing the contour and (3) the number of points on a sampled contour.Interpolation performance was very accurate, comparable to results from Vernier tasks. Setting variability was highest along the line of sight and for the parabolic contour. Setting variability did not decrease with increasing number of points on either contour, suggesting that observers do not use all available, relevant information in this task.

Humans↗