13:30 - 15:00
Mon-A6-Talk II-
Mon-Talk II-
Room: A6
Chair/s:
Simon Merz
Spatial changes of an object over time are usually perceived as motion. Over the years, various perceptual errors have been identified for dynamic, moving objects. These include, but are not limited to, spatial over- or underestimation of the initial or final position (e.g. Fröhlich Effect, Onset-Repulsion Effect, Representational-Momentum Effect, Offset-Repulsion Effect), spatio-temporal discrepancies between moving and stationary objects (Flash-Lag Effect, Flash-Drag Effect) or the interaction between spatial and temporal properties of a dynamic display (e.g. Kappa Effect, Tau Effect). Given the vast amount of different perceptual errors reported over the decades, many theoretical explanations have been proposed. With the common goal of understanding spatio-temporal perception of dynamic objects, the symposium aims to bring together researchers working on the different perceptual biases to enable cross-paradigm perspectives and discussion. The speakers will present experimental work using different experimental procedures, analytical approaches and theoretical background to show current developments in the field, with the final talk in the session allowing general, talk overarching discussions about human spatio-temporal perception and the possible mechanisms underlying these processes.
A paradox of perceived speed and location in the Fröhlich effect
Mon-A6-Talk II-05
Presented by: Pascal Mamassian
Pascal Mamassian
Ecole Normale Supérieure Paris, France
In the Fröhlich effect, the initial position of a moving object tends to be mislocated in its direction of motion. Not too surprisingly, when the duration of the movement is short, the magnitude of the spatial bias is also small (Rubin, 1930). This motion duration property of the Fröhlich effect is a challenge for most existing models that predict little or no effect of duration. We measured localisation biases at the onset of moving objects in a psychophysical experiment using a forced-choice method. To reduce the effects of spatial and temporal predictability, two vertical lines were flashed one above the other at random spatial locations and random times. One of the two lines was set in motion as soon as it appeared, and the other remained static. Observers were instructed to report whether the top line was to the right or the left of the bottom one. Spatial offsets were controlled by interleaved staircases. We found that the magnitude of the spatial bias increases greatly with motion duration and reaches a plateau at about 200ms. Interestingly, before reaching the plateau, spatial biases were almost as large as the full trajectory of the object, suggesting that the moving object was almost perceived static. In a separate experiment, we measured the perceived speed for different durations and found a large over-estimation of perceived speed for durations shorter than about 200ms. Therefore, there seems to be a paradox in that the same moving object appears both almost static and moving very fast.
Keywords: Motion perception, Time perception, Fröhlich effect