Subitizing and Counting by Visual Memory in Dyslexia and Dyscalculia Development – Deficits – Training – Transfer pp. 405-413
Authors: (Burkhart Fischer, Brain Research Unit, Institute of Biophysics, University of Freiburg, Germany)
Abstract: Deficits in auditory or visual perception or in saccade control contribute to problems in acquiring reading and spelling. The corresponding examination of the perceptual and optomotor skills have shown developmental deficits in comparison with age matched control groups (Fischer, Hartnegg, & Mokler, 2000; Fischer et al., 2000; Fischer & Hartnegg, 2004; Biscaldi, Fischer, & Hartnegg, 2000). Selective improvements of these basic skills by daily practice yielded corresponding improvements in reading and spelling (Schäffler, Sonntag, & Fischer, 2004; Fischer & Hartnegg, 2000). This chapter describes the development, deficits, and training effects of a special visual function called subitizing. This function enables subjects to recognize immediately (= subito, lat.) a small number of items even when they were presented only for short periods of time (Mandler & Shebo, 1982; Cowan, 2001; Balakrishnan & Ashby, 1991). Short means, that the time is too short to scan and count the items by saccadic eye movements. Subito means that a counting process is not necessary because the time to recognize one or two or three items is the same. Only when the number of items increases beyond 4 the recognition of the number increases by an almost constant time for each additional item (Jensen, Reese, & Reese, 1950; Trick & Phylyshyn, 1994). This fact indicates, that an internal counting process takes place in the brain. (When we use "counting" we do not mean counting the numbers of items at all, but counting them on the basis of an internal presentation in the memory obtained by a short presentation of the items. Similarly, we will use "subitizing", when talking about the total process of finding the number of items in the task described below).