Saccadic search performance: the effect of element spacing

In a saccadic search task, we investigated whether spacing between elements affects search performance. Since it has been suggested in the literature that element spacing can affect the eye movement strategy in several ways, its effects on search time per element are hard to predict. In the first experiment, we varied the element spacing (3.4°–7.1° distance between elements) and target–distracter similarity. As expected, search time per element increased with target–distracter similarity. Decreasing element spacing decreased the search time per element. However, this effect was surprisingly small in comparison to the effect of varying target–distracter similarity. In a second experiment, we elaborated on this finding and decreased element spacing even further (between 0.8° and 3.2°). Here, we did not find an effect on search time per element for element spacings from 3.2° to spacings as small as 1.5°. It was only at distances smaller than 1.5° that search time per element increased with decreasing element spacing. In order to explain the remarkable finding that search time per element was not affected for such a wide range of element spacings, we propose that irrespective of the spacing crowding kept the number of elements processed per fixation more or less constant.

[1]  H. BOUMA,et al.  Interaction Effects in Parafoveal Letter Recognition , 1970, Nature.

[2]  G. Sperling,et al.  Extremely Rapid Visual Search: The Maximum Rate of Scanning Letters for the Presence of a Numeral , 1971, Science.

[3]  G. McConkie,et al.  The span of the effective stimulus during a fixation in reading , 1975 .

[4]  J. Senders,et al.  Eye Movements and Psychological Processes , 1976 .

[5]  F. L. Engel.  Visual conspicuity, visual search and fixation tendencies of the eye , 1977, Vision Research.

[6]  T. Salthouse,et al.  Determinants of eye-fixation duration. , 1980, The American journal of psychology.

[7]  K Moffitt,et al.  Evaluation of the fixation duration in visual search , 1980, Perception & psychophysics.

[8]  Heino Widdel,et al.  Eye Movement Measurement in the Assessment and Training of Visual Performance , 1981 .

[9]  J. Moraal,et al.  Manned systems design : methods, equipment, and applications , 1981 .

[10]  G Wolford,et al.  Lateral masking as a function of spacing , 1983, Perception & psychophysics.

[11]  Arthur M. Jacobs,et al.  The effect of visibility on eye-movement parameters in reading , 1983, Perception & psychophysics.

[12]  A. Jacobs.  Eye-movement control in visual search: How direct is visual span control? , 1986, Perception & psychophysics.

[13]  Donald L. Fisher,et al.  EYE MOVEMENTS AND THE PERCEPTUAL SPAN DURING VISUAL SEARCH , 1987 .

[14]  K Rayner,et al.  Letter processing during eye fixations in visual search , 1987, Perception & psychophysics.

[15]  Wolfgang Prinz,et al.  Saccade amplitude determines fixation duration: Evidence from continuous search , 1987 .

[16]  J. O'Regan.  Eye movements and reading. , 1990, Reviews of oculomotor research.

[17]  D. Levi,et al.  The two-dimensional shape of spatial interaction zones in the parafovea , 1992, Vision Research.

[18]  Tatjana A. Nazir,et al.  Effects of lateral masking and spatial precueing on gap-resolution in central and peripheral vision , 1992, Vision Research.

[19]  D. Pelli,et al.  The information capacity of visual attention , 1992, Vision Research.

[20]  D. Levi,et al.  The effect of similarity and duration on spatial interaction in peripheral vision. , 1994, Spatial vision.

[21]  J. Steen,et al.  Unequal amplitude saccades produced by aniseikonic patterns: Effects of viewing distance , 1995, Vision Research.

[22]  M. Carrasco,et al.  The eccentricity effect: Target eccentricity affects performance on conjunction searches , 1995, Perception & psychophysics.

[23]  P. Cavanagh,et al.  Attentional resolution and the locus of visual awareness , 1996, Nature.

[24]  C. J. Erkelens,et al.  Control of fixation duration in a simple search task , 1996, Perception & psychophysics.

[25]  D H Brainard,et al.  The Psychophysics Toolbox. , 1997, Spatial vision.

[26]  D G Pelli,et al.  The VideoToolbox software for visual psychophysics: transforming numbers into movies. , 1997, Spatial vision.

[27]  J. Wolfe,et al.  Why are there eccentricity effects in visual search? Visual and attentional hypotheses , 1998, Perception & psychophysics.

[28]  B. C. Motter,et al.  The guidance of eye movements during active visual search , 1998, Vision Research.

[29]  C. Scialfa,et al.  Response times and eye movements in feature and conjunction search as a function of target eccentricity , 1998, Perception & psychophysics.

[30]  K. Rayner.  Eye movements in reading and information processing: 20 years of research. , 1998, Psychological bulletin.

[31]  B. C. Motter,et al.  The zone of focal attention during active visual search , 1998, Vision Research.

[32]  C. Erkelens,et al.  Peripheral vision and oculomotor control during visual search , 1999, Vision Research.

[33]  J. H. Bertera,et al.  Eye movements and the span of the effective stimulus in visual search , 2000, Perception & psychophysics.

[34]  Ilpo Kojo,et al.  Effect of stimulus contrast on performance and eye movements in visual search , 2001, Vision Research.

[35]  Susana T. L. Chung,et al.  Spatial-frequency and contrast properties of crowding , 2001, Vision Research.

[36]  M. A. Frens,et al.  Recording eye movements with video-oculography and scleral search coils: a direct comparison of two methods , 2002, Journal of Neuroscience Methods.

[37]  Frans W Cornelissen,et al.  The Eyelink Toolbox: Eye tracking with MATLAB and the Psychophysics Toolbox , 2002, Behavior research methods, instruments, & computers : a journal of the Psychonomic Society, Inc.