title: A first- and second-order motion energy analysis of peripheral motion illusions leads to further evidence of "feature blur" in peripheral vision.
abstract: BACKGROUND
  Anatomical and physiological differences between the central and peripheral visual systems are well documented. Recent findings have suggested that vision in the periphery is not just a scaled version of foveal vision, but rather is relatively poor at representing spatial and temporal phase and other visual features. Shapiro, Lu, Huang, Knight, and Ennis (2010) have recently examined a motion stimulus (the "curveball illusion") in which the shift from foveal to peripheral viewing results in a dramatic spatial/temporal discontinuity. Here, we apply a similar analysis to a range of other spatial/temporal configurations that create perceptual conflict between foveal and peripheral vision.
  
  
  RESULTS
  To elucidate how the differences between foveal and peripheral vision affect super-threshold vision, we created a series of complex visual displays that contain opposing sources of motion information. The displays (referred to as the peripheral escalator illusion, peripheral acceleration and deceleration illusions, rotating reversals illusion, and disappearing squares illusion) create dramatically different perceptions when viewed foveally versus peripherally. We compute the first-order and second-order directional motion energy available in the displays using a three-dimensional Fourier analysis in the (x, y, t) space. The peripheral escalator, acceleration and deceleration illusions and rotating reversals illusion all show a similar trend: in the fovea, the first-order motion energy and second-order motion energy can be perceptually separated from each other; in the periphery, the perception seems to correspond to a combination of the multiple sources of motion information. The disappearing squares illusion shows that the ability to assemble the features of Kanisza squares becomes slower in the periphery.
  
  
  CONCLUSIONS
  The results lead us to hypothesize "feature blur" in the periphery (i.e., the peripheral visual system combines features that the foveal visual system can separate). Feature blur is of general importance because humans are frequently bringing the information in the periphery to the fovea and vice versa.
authors.affiliation: Department of Psychology, American University, Washington, DC, United States of America. Arthur.Shapiro@american.edu
authors.forename: Arthur G
authors.initials: AG
authors.lastname: Shapiro
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Knight
authors.forename: Zhong-Lin
authors.initials: ZL
authors.lastname: Lu
mesh_terms: D000054:Acceleration; D000328:Adult; D005583:Fourier Analysis; D005584:Fovea Centralis / Q000502:physiology; D006801:Humans; D009038:Motion; D009039:Motion Perception / Q000502:physiology; D010465:Perception; D012984:Software; D013028:Space Perception; D013997:Time Factors; D014785:Vision, Ocular / Q000502:physiology*; D014794:Visual Fields