title: Both vision-for-perception and vision-for-action follow Weber's law at small object sizes, but violate it at larger sizes.
abstract: According to a previous report, the visual coding of size does not obey Weber's law when aimed at guiding a grasp (Ganel et al., 2008a). This result has been interpreted as evidence for a fundamental difference between sensory processing in vision-for-perception, which needs to compress a wide range of physical objects to a restricted range of percepts, and vision-for-action when applied to the much narrower range of graspable and reachable objects. We compared finger aperture in a motor task (precision grip) and perceptual task (cross modal matching or "manual estimation" of the object's size). Crucially, we tested the whole range of graspable objects. We report that both grips and estimations clearly violate Weber's law with medium-to-large objects, but are essentially consistent with Weber's law with smaller objects. These results differ from previous characterizations of perception-action dissociations in the precision of representations of object size. Implications for current functional interpretations of the dorsal and ventral processing streams in the human visual system are discussed.
authors.affiliation: Università di Parma, Italy. Electronic address: nicola.bruno@unipr.it.
authors.forename: Nicola
authors.initials: N
authors.lastname: Bruno
authors.affiliation: Università di Parma, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Uccelli
authors.affiliation: Università di Parma, Italy.
authors.forename: Eva
authors.initials: E
authors.lastname: Viviani
authors.affiliation: Università Vita-Salute S. Raffaele and Experimental Psychology Unit, Division of Neuroscience, IRCCS San Raffaele Scientific Institute, Milano, Italy.
authors.forename: Claudio
authors.initials: C
authors.lastname: de'Sperati
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004056:Differential Threshold / Q000502:physiology*; D005260:Female; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D010775:Photic Stimulation; D011597:Psychomotor Performance / Q000502:physiology*; D012858:Size Perception / Q000502:physiology*; D013997:Time Factors; D014785:Vision, Ocular / Q000502:physiology*; D055815:Young Adult
keywords: Accuracy; Action; Manual estimation; Perception; Precision; Precision grip; Weber's law