On the effective number of tracked trajectories in normal human vision.
Tripathy, Srimant P. Narasimhan, Sathyasri Barrett, Brendan T.
Tripathy, Srimant P.
Narasimhan, Sathyasri
Barrett, Brendan T.
Publication Date
2007
End of Embargo
Supervisor
Rights
Peer-Reviewed
Yes
Open Access status
closedAccess
Accepted for publication
Institution
Department
Awarded
Embargo end date
Collections
Additional title
Abstract
Z. W. Pylyshyn and R. W. Storm (1988) have shown that human observers can accurately track four to five items at a time. However, when a threshold paradigm is used, observers are unable to track more than a single trajectory accurately (S. P. Tripathy & B. T. Barrett, 2004). This difference between the two studies is examined systematically using substantially suprathreshold stimuli. The stimuli consisted of one (Experiment 1) or more (Experiments 2 and 3) bilinear target trajectories embedded among several linear distractor trajectories. The target trajectories deviated clockwise (CW) or counterclockwise (CCW) (by 19°, 38°, or 76° in Experiments 1 and 2 and by 19°, 38°, or 57° in Experiment 3), and observers reported the direction of deviation. From the percentage of correct responses, the ¿effective¿ number of tracked trajectories was estimated for each experimental condition. The total number of trajectories in the stimulus and the number of deviating trajectories had only a small effect on the effective number of tracked trajectories; the effective number tracked was primarily influenced by the angle of deviation of the targets and ranged from four to five trajectories for a ±76° deviation to only one to two trajectories for a ±19° deviation, regardless of whether the different magnitudes of deviation were blocked (Experiment 2) or interleaved (Experiment 3). Simple hypotheses based on ¿averaging of orientations,¿ ¿preallocation of resources,¿ or pop-out, crowding, or masking of the target trajectories are unlikely to explain the relationship between the effective number tracked and the angle of deviation of the target trajectories. This study reconciles the difference between the studies cited above in terms of the number of trajectories that can be tracked at a time.
Version
No full-text in the repository
Citation
Tripathy, S.R., Narasimhan, S. and Barrett, B.T. (2007). On the effective number of tracked trajectories in normal human vision. Journal of Vision. Vol. 7, No. 6, pp. 1-18.
Link to publisher’s version
Link to published version
Link to Version of Record
Type
Article