title: Fast moving texture has opposite effects on the perceived speed of visible and occluded object trajectories.
abstract: In a series of psychophysical experiments, we altered the perceived speed of a spot (target) using a grayscale texture moving in the same (iso-motion) or opposite (anti-motion) direction of the target. In Experiment 1, using a velocity discrimination task (2IFC), the target moved in front of the texture and was perceived faster with anti-motion than iso-motion texture. The integration and segregation of motion signals in high-level motion areas may have accounted for the illusion. In Experiment 2, by asking observers to estimate the time-to-contact (TTC) with a bar indicating the end of the invisible trajectory, we showed that this illusory visible speed, due to anti- (iso-) texture, reduced (increased) the subsequent estimated duration of occluded target trajectory. However, in Experiment 3, when the target disappeared behind the iso-motion texture, the TTC was estimated shorter than anti- and static textures. In Experiment 4, using an interruption paradigm, we found negative Point of Subjective Equalities (PSEs) with iso-motion but not static texture, suggesting that iso-motion led to overestimation of the hidden speed. However, sensitivity to target speed differences, as assessed by JNDs and d'values was not affected. Results of Experiments 3 and 4 indicate that only the iso-texture affected the estimated target speed, but with opposite polarity compared to visible motion, suggesting a different origin of speed bias. Because our results show that visuospatial tracking was facilitated by the fast iso-motion, we conclude that motion of the occluded target was tracked by shifting visuospatial attention.
authors: Department of General Psychology, University of Padova, Via Venezia 8, 35131 Padova, Italy. Electronic address: luca.battaglini@unipd.it.
authors: Luca
authors: L
authors: Battaglini
authors: Department of General Psychology, University of Padova, Via Venezia 8, 35131 Padova, Italy.
authors: Giulio
authors: G
authors: Contemori
authors: Centre de Recherche Cerveau & Cognition (CerCo), Toulouse, France; University of California, Riverside, Department of Psychology, Riverside, CA, USA.
authors: Marcello
authors: M
authors: Maniglia
authors: Department of General Psychology, University of Padova, Via Venezia 8, 35131 Padova, Italy.
authors: Clara
authors: C
authors: Casco
mesh_terms: D000328:Adult; D004192:Discrimination, Psychological / Q000502:physiology*; D005260:Female; D006801:Humans; D007088:Illusions; D008297:Male; D009038:Motion; D009039:Motion Perception / Q000502:physiology*; D010364:Pattern Recognition, Visual; D011597:Psychomotor Performance / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult
keywords: Invisible motion; Motion; Perceived speed; Surround motion; Texture