Unimodal and bimodal numerosity judgments
Poster Presentation

Alberto Gallace
Department of Experimental Psychology, Oxford University, Oxford, UK

Hong Z. Tan
Haptic Interface Research Laboratory, Purdue University, West Lafayette, USA

Charles Spence
Department of Experimental Psychology, Oxford University, Oxford, UK

     Abstract ID Number: 37
     Full text: Not available
     Last modified: March 15, 2005

Abstract
Numerosity judgment research reveals a discontinuity in judgments of small (≤4) versus large (>4) numbers of visual stimuli, consistent with people shifting from a strategy of subitizing to one of counting. In Experiment 1, we explored “tactile” numerosity judgments, briefly presenting 1-7 vibrotactile stimuli over the body surface. The accuracy of participants’ estimates of the number of tactile stimuli presented decreased linearly as a function of the number of locations stimulated. However, no evidence of a discontinuity in tactile numerosity judgments was observed (arguing against subitization in tactile perception). In Experiment 2, we investigated numerosity judgments using both unimodal and bimodal displays consisting of 1-6 vibrotactile stimuli (presented over the body surface) and 1-6 visual stimuli (seen on the body via mirror reflection). Participants had to count the number of stimuli regardless of their modality of presentation. The accuracy of bimodal numerosity judgments was not predicted by performance on the unimodal displays. In fact, bimodal numerosity judgments were significantly worse than those for unimodal displays of equivalent number. These counterintuitive results are discussed in relation to current theories of crossmodal integration and to the cognitive resources and/or common spatial representations possibly accessed by visual and tactile stimuli.