The Journal of Neuroscience, October 1, 2002, 22(19):8661-8664
Direct Evidence That "Speedlines" Influence Motion Mechanisms
David C.
Burr1, 2 and
John
Ross3
1 Istituto di Neurofisiologia del Consiglio Nazionale
delle Ricerche, Pisa 56100, Italy, 2 Dipartimento di
Psicologia, Università di Firenze, Firenze 50125, Italy, and
3 School of Psychology, University of Western Australia,
Perth, Western Australia 6009, Australia
Determining the direction of visual motion poses a serious problem
for any visual system, given the inherent ambiguities. Geisler (1999)
has suggested that motion streaks left in the wake of a moving target
provide a rich source of potential information that could aid in
resolving direction ambiguities. Here we provide strong experimental
evidence that the human visual system does in fact exploit motion
streaks in direction discrimination. Masks comprising oriented random
noise impeded direction discrimination of moving dots when the masks
were oriented parallel to the direction of motion but had very little
effect when oriented orthogonal to the direction of motion. The masking
effect decreased systematically with increasing bandwidth for the
parallel masks and increased with bandwidth for the orthogonal masks.
Importantly, these masks had little effect on neither contrast
sensitivity for detecting the moving stimuli nor for speed
discrimination. Experiments with "Glass patterns" (moiré
patterns constructed from random dot pairs) confirmed that misleading
pattern information can impede motion detection. The results show that
the oriented streaks left by moving stimuli provide fundamental
information about the direction of visual motion; removing these
streaks or augmenting them with erroneous streaks severely confounds
motion direction discrimination.
Key words:
vision; motion; middle temporal; motion streaks; motion
blur; speedlines
Copyright © 2002 Society for Neuroscience 0270-6474/02/22198661-04$05.00/0