Disturbance of attention has been frequently suggested as one of the mechanisms underlying schizophrenic thought disorder (Weckowicz and Blewett, 1959; Chapman, 1961; Payne, 1966). Much effort has, therefore, been directed toward studying this variable in schizophrenia (McGhie, 1971; Neale and Cromwell, 1972). The approach undertaken has been determined by the psychophysiological and theoretical constructs presumed to be involved. To enumerate a few, disordered attention has been studied with indices of arousal (Venables, 1960; Venables and Wing, 1962), vigilance tasks (Mackworth, 1970), reaction time (Shakow, 1962), size constancy (Weckowicz and Blewett, 1959; Silverman, 1964a), tachistoscopic detection (Kornetsky, 1972), the WAIS Digit Span subtest (Blum et al., 1969), and immediate recall (McGhie et al., 1965). The lack of correspondence between these various procedures has become increasingly apparent (Neale and Cromwell, 1972). In one recent study, for example, the intercorrelations of five purported measures of attention ranged from –.23 to +.31 (Kopfstein and Neale, 1972).