Localization of shapes: eye movements and perception compared

The localization of spatially extended objects is thought to be based on the computation of a default reference position, such as the center of gravity. This position can serve as the goal point for a saccade, a locus for fixation, or the reference for perceptual localization. We compared perceptual and saccadic localization for non-convex shapes where the center of gravity (COG) was located outside the boundary of the shape and did not coincide with any prominent perceptual features. The landing positions of single saccades made to the shape, as well as the preferred loci for fixation, were near the center of gravity, although local features such as part boundaries were influential. Perceptual alignment positions were also close to the center of gravity, but showed configural effects that did not influence either saccades or fixation. Saccades made in a more naturalistic sequential scanning task landed near the center of gravity with a considerably higher degree of accuracy (mean error <4% of saccade size) and showed no effects of local features, constituent parts, or stimulus configuration. We conclude that perceptual and oculomotor localization is based on the computation of a precise central reference position, which coincides with the center of gravity in sequential scanning. The saliency of the center of gravity, relative to other prominent visual features, can depend on the specific localization task or the relative configuration of elements. Sequential scanning, the more natural of the saccadic tasks, may provide a better way to evaluate the "default" reference position for localization. The fact that the reference position used in both oculomotor and perceptual tasks fell outside the boundary of the shapes supports the importance of spatial pooling, in contrast to local features, in object localization.

[1]  Eileen Kowler,et al.  Saccadic localization of occluded targets , 2000, Vision Research.

[2]  Erik Blaser,et al.  The accuracy and precision of saccades to small and large targets , 1995, Vision Research.

[3]  H. Collewijn,et al.  Differences in accuracy of human saccades between stationary and jumping targets , 1989, Vision Research.

[4]  D. Proffitt,et al.  The roles of contour and luminance distribution in determining perceived centers within shapes , 1983, Perception & psychophysics.

[5]  John M. Findlay,et al.  The spatial signal for saccadic eye movements emphasizes visual boundaries , 1993, Perception & psychophysics.

[6]  D. Whitaker,et al.  Centroid evaluation in the vernier alignment of random dot clusters , 1988, Vision Research.

[7]  L. Kaufman,et al.  Spontaneous fixation tendencies for visual forms , 1969 .

[8]  D. Levi,et al.  Localization of a Peripheral Patch: The Role of Blur and Spatial Frequency , 1996, Vision Research.

[9]  Eileen Kowler,et al.  The role of location probability in the programming of saccades: Implications for “center-of-gravity” tendencies , 1989, Vision Research.

[10]  A. A. Skavenski,et al.  Miniature eye movement. , 1973, Science.

[11]  Suzanne P. McKee,et al.  Integration regions for visual hyperacuity , 1977, Vision Research.

[12]  P. Glimcher,et al.  Representation of averaging saccades in the superior colliculus of the monkey , 1993, Experimental Brain Research.

[13]  J. Cronly-Dillon,et al.  Vision and visual dysfunction. , 1994, Journal of cognitive neuroscience.

[14]  Eileen Kowler,et al.  Shapes, surfaces and saccades , 1999, Vision Research.

[15]  Eileen Kowler,et al.  The effect of expectations on slow oculomotor control—II. Single target displacements , 1979, Vision Research.

[16]  D. Levi,et al.  Spatial localization without visual references , 1992, Vision Research.

[17]  E Kowler,et al.  Saccadic localization of eccentric forms. , 1991, Journal of the Optical Society of America. A, Optics and image science.

[18]  Ronald M. Hansen,et al.  Spatial localization during pursuit eye movements , 1979, Vision Research.

[19]  Dennis M. Levi,et al.  Collinearity improves alignment Response to Keeble and Hess (1998) , 2002, Vision Research.

[20]  Christian Coëffé,et al.  Reducing the influence of non-target stimuli on saccade accuracy: Predictability and latency effects , 1987, Vision Research.

[21]  H. Collewijn,et al.  The function of visual search and memory in sequential looking tasks , 1995, Vision Research.

[22]  F. Ottes,et al.  Latency dependence of colour-based target vs nontarget discrimination by the saccadic system , 1985, Vision Research.

[23]  Eileen Kowler,et al.  Saccadic localization of random dot targets , 1998, Vision Research.

[24]  Vision Research , 1961, Nature.

[25]  D M Levi,et al.  Selective Attention to Specific Location Cues: The Peak and Center of a Patch are Equally Accessible as Location Cues , 1998, Perception.

[26]  Eileen Kowler.  Eye movements and their role in visual and cognitive processes. , 1990, Reviews of oculomotor research.

[27]  Brian J. Murphy,et al.  Simple forms and fluctuations of the line of sight: Implications for motor theories of form processing , 1974 .

[28]  J. O'regan,et al.  Eye fixations near corners: evidence for a centre of gravity calculation based on contrast, rather than luminance or curvature , 1994, Vision Research.

[29]  R. Carpenter,et al.  Movements of the Eyes , 1978 .

[30]  M. Morgan,et al.  Biases and sensitivities in geometrical illusions , 1990, Vision Research.

[31]  R. Steinman.  Effect of Target Size, Luminance, and Color on Monocular Fixation* , 1965 .

[32]  J. Findlay.  Global visual processing for saccadic eye movements , 1982, Vision Research.

[33]  Eileen Kowler,et al.  The control of saccadic adaptation: implications for the scanning of natural visual scenes , 2000, Vision Research.

[34]  Melvyn A. Goodale,et al.  The cortical organization of visual perception and visuomotor control , 1995 .

[35]  H Collewijn,et al.  Binocular eye movements and the perception of depth. , 1990, Reviews of oculomotor research.

[36]  H. D. Crane,et al.  Accurate three-dimensional eyetracker. , 1978, Applied optics.

[37]  Eric Mjolsness,et al.  A center-of-mass computation describes the precision of random dot displacement discrimination , 1992, Vision Research.

[38]  L. Kaufman,et al.  “Center-of-gravity” Tendencies for fixations and flow patterns , 1969 .

[39]  DAVID WHITAKER,et al.  Centroid Analysis Predicts Visual Localization of First- and Second-order Stimuli , 1996, Vision Research.

[40]  Milan Vego,et al.  Center of Gravity , 2000 .

[41]  D. R. T. Keeble,et al.  PII: S0042-6989(97)00234-4 , 2003 .

[42]  Carolina M. Zingale,et al.  Planning sequences of saccades , 1987, Vision Research.

[43]  Rajesh P. N. Rao,et al.  Embodiment is the foundation, not a level , 1996, Behavioral and Brain Sciences.

[44]  David Whitaker,et al.  The effect of suprathreshold contrast on stimulus centroid and its implications for the perceived location of objects , 1998, Vision Research.

[45]  J. V. Gisbergen,et al.  Collicular ensemble coding of saccades based on vector summation , 1987, Neuroscience.

[46]  S. Coren,et al.  Effect of Non-Target Stimuli upon Length of Voluntary Saccades , 1972, Perceptual and motor skills.

[47]  Dennis M. Levi,et al.  Collinearity improves alignment. Authors' reply , 2002 .

[48]  N BOCHEVA,et al.  Different Mechanisms may Underlie the Performance in Relative Localization Tasks , 1996, Vision Research.

[49]  D. Sparks,et al.  Population coding of saccadic eye movements by neurons in the superior colliculus , 1988, Nature.

[50]  Paul V. McGraw,et al.  Alignment of separated patches: multiple location tags , 1999, Vision Research.

[51]  B. Dosher,et al.  The role of attention in the programming of saccades , 1995, Vision Research.