title: Visual imagery selectively reduces vernier acuity.
abstract: Mental imagery interferes with perception. This, an example of the 'Perky effect', was studied for vernier acuity. Mean accuracy for reporting the offset of vertical line targets declined from 80% to 65% when subjects were requested to imagine vertical lines near fixation. Images of horizontal lines or of a grey mist in the fixation region lowered accuracy to a similar extent. However, accuracy was barely affected when the image was requested 1.5 deg or more from the target. The Perky effect remained strong for at least 4 s after an instruction to 'clear' the image away. The results were not due to imagery-induced changes in fixation, pupil diameter, or accommodation, or (at least primarily) to central attentional or decisional factors. Rather, imagery produces a local, pattern-insensitive, and relatively long-lasting reduction in visual sensitivity. The sensitivity loss may be mimicked by a 0.24 log unit reduction in target energy.
authors.affiliation: Northeastern University, Boston, MA 02115.
authors.forename: C
authors.initials: C
authors.lastname: Craver-Lemley
authors.forename: A
authors.initials: A
authors.lastname: Reeves
mesh_terms: D005403:Fixation, Ocular; D006801:Humans; D007092:Imagination; D012399:Rotation; D013028:Space Perception; D013997:Time Factors; D014792:Visual Acuity; D014796:Visual Perception