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Time-to-Collision (TTC) judgements with offsize objects show that Tau needs to be intergrated with familiar size to explain TTC performance

conference contribution
posted on 2003-01-01, 00:00 authored by Simon Hosking, Boris Crassini
Observers judged TTC with computer-generated displays simulating an approaching object in three familiar-size conditions:

(i) Real-size (smaller, larger objects depicted as tennis, soccer balls respectively).
(ii) Off-size (smaller, larger objects depicted as soccer, tennis balls respectively).
(iii) Ambiguous-size (smaller, larger objects depicted as texture-less black balls of different size).

Displays simulated objects approaching observersí viewpoint from 24.96 m, and disappearing at 5.76 m. Manipulation of approach velocities (4.8-19.2 msec-1) produced viewing times from 1.0 to 4.0 sec, and delays between object disappearance and tau-based TTC ranging from 0.3 to 1.2 sec. Motion characteristics of smaller and larger objects in the three familiar-size conditions simulated those of approaching real-sized tennis and soccer balls respectively; that is, for each approach velocity, tau‚-based TTC was the same across the three conditions for smaller and larger objects.

Results showed that, consistent with the proposition of tau-determined TTC, TTC estimates in the real-size condition were uninfluenced by object size. This is contrary to previous reports that TTC for larger objects is underestimated relative to TTC for smaller objects. However, such size-dependent TTC differences were found in the ambiguous-size condition, with even larger differences in the off-size condition; TTCs for the ëlargerí tennis ball were much less than TTCs to the ësmallerí soccer ball compared to corresponding TTCs in the ambiguous-size condition. These results are problematic for the proposition that tau solely determines TTC. We discuss the role of perceptual learning in resolving this problem.



International Conference on Perception and Action (12th : 2003 : Gold Coast, Qld.)


51 - 51


Lawrence Erlbaum Associates


Gold Coast, Qld.

Place of publication

Mahwah, N.J.

Start date


End date








Publication classification

E3 Extract of paper


S Rogers, J Effken

Title of proceedings

Studies in perception and action VII : twelfth International conference on perception and action, July 13-18, 2003, Gold Coast, Queensland, Australia

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