Grasping and Pointing — Visual Conflict and Interference

There have been many debates of the two-visual-systems (whatvs. how or perceptionvs. action) hypothesis that was proposed by Goodale and his colleagues. Many researchers have provided a variety of evidence for or against the hypothesis. For instance, a study performed by Agliotiet al. offered good evidence for the two-visual-systems theory using the Ebbinghaus illusion, but some researchers who used other visual illusions failed to find consistent results. Therefore, we used a perceptual task of conflict or interference to test this hypothesis. If the conflict or interference in perception had an influence on the processing of perception alone and did not affect the processing of action, we could infer that the two visual systems are separated, and vice versa. In the current study, we carried out two experiments which employed the Stroop, Garner and SNARC paradigms and used graspable 3-D Arabic numerals. We aimed to find if the effects resulting from perceptual conflicts or interferences would affect participants’ grasping and pointing. The results showed that the interaction between Stroop and numeral order (ascending or descending, or SNARC) was significant, and the SNARC effect significantly affected action, but the main effects of Stroop and Garner interference were not significant. The results indicated that, to some degree, perceptual conflict affects action processing. The results did not provide evidence for two separate visual systems.

Lower Pitch Is Larger, Yet Falling Pitches Shrink

Experiments using diverse paradigms, including speeded discrimination, indicate that pitch and visually-perceived size interact perceptually, and that higher pitch is congruent with smaller size. While nearly all of these studies used static stimuli, here we examine the interaction of dynamic pitch and dynamic size, using Garner’s speeded discrimination paradigm. Experiment 1 examined the interaction of continuous rise/fall in pitch and increase/decrease in object size. Experiment 2 examined the interaction of static pitch and size (steady high/low pitches and large/small visual objects), using an identical procedure. Results indicate that static and dynamic auditory and visual stimuli interact in opposite ways. While for static stimuli (Experiment 2), higher pitch is congruent with smaller size (as suggested by earlier work), for dynamic stimuli (Experiment 1), ascending pitch is congruent with growing size, and descending pitch with shrinking size. In addition, while static stimuli (Experiment 2) exhibit both congruence and Garner effects, dynamic stimuli (Experiment 1) present congruence effects without Garner interference, a pattern that is not consistent with prevalent interpretations of Garner’s paradigm. Our interpretation of these results focuses on effects of within-trial changes on processing in dynamic tasks and on the association of changes in apparent size with implied changes in distance. Results suggest that static and dynamic stimuli can differ substantially in their cross-modal mappings, and may rely on different processing mechanisms.