Abstract
In two experiments, we demonstrate a misperception of the velocity of a random-dot stimulus moving in the presence of a static line oriented obliquely to the direction of dot motion. As shown in previous studies, the perceived direction of the dots is shifted away from the orientation of the static line, with the size of the shift varying as a function of line orientation relative to dot direction (the statically-induced direction illusion, or 'SDI'). In addition, we report a novel effect - that perceived speed also varies as a function of relative line orientation, decreasing systematically as the angle is reduced from 90° to 0°. We propose that these illusions both stem from the differential processing of object-relative and non-object-relative component velocities, with the latter being perceptually underestimated with respect to the former by a constant ratio. Although previous proposals regarding the SDI have not allowed quantitative accounts, we present a unified formal model of perceived velocity (both direction and speed) with the magnitude of this ratio as the only free parameter. The model was successful in accounting for the angular repulsion of motion direction across line orientations, and in predicting the systematic decrease in perceived velocity as the line's angle was reduced. Although fitting for direction and speed produced different best-fit values of the ratio of underestimation of non-object-relative motion compared to object-relative motion (with the ratio for speed being larger than that for direction) this discrepancy may be due to differences in the psychophysical procedures for measuring direction and speed.
| Language | English |
|---|---|
| Pages | 10-18 |
| Number of pages | 9 |
| Journal | Vision Research |
| Volume | 92 |
| DOIs | |
| Publication status | Published - 2013 |
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Bibliographical note
Erratum can be found at Vision Research volume 96, p150, https://doi.org/10.1016/j.visres.2013.10.022Keywords
- differential processing
- statically-induced direction illusion
- relative motion
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Differential processing : towards a unified model of direction and speed perception. / Farrell-Whelan, Max; Brooks, Kevin R.
In: Vision Research, Vol. 92, 2013, p. 10-18.Research output: Contribution to journal › Article › Research › peer-review
TY - JOUR
T1 - Differential processing
T2 - Vision Research
AU - Farrell-Whelan, Max
AU - Brooks, Kevin R.
N1 - Erratum can be found at Vision Research volume 96, p150, https://doi.org/10.1016/j.visres.2013.10.022
PY - 2013
Y1 - 2013
N2 - In two experiments, we demonstrate a misperception of the velocity of a random-dot stimulus moving in the presence of a static line oriented obliquely to the direction of dot motion. As shown in previous studies, the perceived direction of the dots is shifted away from the orientation of the static line, with the size of the shift varying as a function of line orientation relative to dot direction (the statically-induced direction illusion, or 'SDI'). In addition, we report a novel effect - that perceived speed also varies as a function of relative line orientation, decreasing systematically as the angle is reduced from 90° to 0°. We propose that these illusions both stem from the differential processing of object-relative and non-object-relative component velocities, with the latter being perceptually underestimated with respect to the former by a constant ratio. Although previous proposals regarding the SDI have not allowed quantitative accounts, we present a unified formal model of perceived velocity (both direction and speed) with the magnitude of this ratio as the only free parameter. The model was successful in accounting for the angular repulsion of motion direction across line orientations, and in predicting the systematic decrease in perceived velocity as the line's angle was reduced. Although fitting for direction and speed produced different best-fit values of the ratio of underestimation of non-object-relative motion compared to object-relative motion (with the ratio for speed being larger than that for direction) this discrepancy may be due to differences in the psychophysical procedures for measuring direction and speed.
AB - In two experiments, we demonstrate a misperception of the velocity of a random-dot stimulus moving in the presence of a static line oriented obliquely to the direction of dot motion. As shown in previous studies, the perceived direction of the dots is shifted away from the orientation of the static line, with the size of the shift varying as a function of line orientation relative to dot direction (the statically-induced direction illusion, or 'SDI'). In addition, we report a novel effect - that perceived speed also varies as a function of relative line orientation, decreasing systematically as the angle is reduced from 90° to 0°. We propose that these illusions both stem from the differential processing of object-relative and non-object-relative component velocities, with the latter being perceptually underestimated with respect to the former by a constant ratio. Although previous proposals regarding the SDI have not allowed quantitative accounts, we present a unified formal model of perceived velocity (both direction and speed) with the magnitude of this ratio as the only free parameter. The model was successful in accounting for the angular repulsion of motion direction across line orientations, and in predicting the systematic decrease in perceived velocity as the line's angle was reduced. Although fitting for direction and speed produced different best-fit values of the ratio of underestimation of non-object-relative motion compared to object-relative motion (with the ratio for speed being larger than that for direction) this discrepancy may be due to differences in the psychophysical procedures for measuring direction and speed.
KW - differential processing
KW - statically-induced direction illusion
KW - relative motion
UR - http://www.scopus.com/inward/record.url?scp=84884329762&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/record.url?scp=84896729422&partnerID=8YFLogxK
UR - https://doi.org/10.1016/j.visres.2013.10.022
U2 - 10.1016/j.visres.2013.08.010
DO - 10.1016/j.visres.2013.08.010
M3 - Article
VL - 92
SP - 10
EP - 18
JO - Vision Research
JF - Vision Research
SN - 0042-6989
ER -