[Spatial resolution gradient of the visual field and flexibility of visual sampling].
This study investigated retinal eccentricity effects in visual search. We introduced several scaling methods for the spatial resolution gradient (SRG) of the visual field induced by retinal properties. Each of stimuli in a single trial was presented at various eccentricities instantaneously. In M-scaling, the stimuli were gradually magnified as increasing eccentricity to compensate for the peripheral reduction in spatial resolution (Rovamo & Virsu, 1979). In Unscaling and D-scaling, the minimum and maximum sizes in M-scaling were used respectively regardless of eccentricity. D-scaling improved the visibility of peripheral stimuli while preserving the SRG. Using a search asymmetry for notched and complete squares, we arranged two tasks with different degrees of target discriminability. The search performance of both tasks became increasingly less efficient as the target appeared at more distant eccentricities in Unscaling, but M-scaling reduced the eccentricity effect. However, D-scaling produced efficient search for the salient target regardless of eccentricity, but held the eccentricity effect in the difficult search. On the SRG, the visual system seems to achieve a balance between simultaneous visual sampling over a wide field of vision and attentional prioritization of central vision.
Shirama
Aya
A
Graduate School of Humanities aod Sciences, Department of Psychology, Ochanomizu University, Ohtsuka, Bunkyo-ku, Tokyo 112-8610, Japan. shirama@jcom.home.ne.jp
Ishiguchi
Akira
A
D006801:Humans; D012160:Retina / Q000502:physiology*; D014794:Visual Fields; D014796:Visual Perception / Q000502:physiology*