Neglect with which they are confronted has been studied sensations into mental representations occur within the most in the context of line bisection (Bisiach the central nervous system and not simply at the Bulgarelli Sterzi vallar 1983)Patients make level of sensory receptors,as implied by Stevens larger errors on larger lines.Marshall and Halligan (1972). demonstrated that psychophysical laws could de- Crossover in Neglect Halligan and Marshall (Halligan Marshall,1988; Marshall Halligan.1989)discovered that patients single-word reading tasks,and weight judgm with neglect ter nded to bisect short lines to the an be mathe atically left of the obie ctive midnoint an wd to d 10051008. m e ipsilesional with the et al 1994a.1992b:Chatter This is found in n (Chat jee et al..1994a)with and is sents the objective ma itude of the stim plain sily b In f h e aw refe d to ed pain in th fo neglecthcorist on sing em unction relati nship are ob atie asks. the con ate judgments of m left (S bjective length 1970 nt o hat mental rep behavic a stin o the physi mental repr ents ha n on idea ha plausibl 1n& ccur in the normal judgments of luminance putationa (Monaghan 8 magnitudes suggest that mental representations are compressed in relation to the ange of the physica The crossover in line bisection is also influenced stimulus.Exponents greater thar one.as in judg by the context in which these lines are seen.Thus ments of pain intensity.suggest that tmental repre patients are more likely to cross and bisec sentations are expanded in relation to the range of to the left of the true midpoint if these the physical stimulus are preceded by a longe line (Marshall, Chatterjee and colleagues showed that patients Krakauer.Sharma.1998).Recently.Chatterie with neglect,across a variety of tasks,have power and colleagues(Chatterjee,Ricci,Calhoun,2000 functions with exponents that are lower than those 1998)showed that of normal patients.These observations suggest crossoverlike phenomenon also occurs with weight that while patients remain sensitive to changes in judgments.Patients in general are likely to judg sensory magnitudes.their awareness of the size of right-sided weights as heavier than left-sided these changes is blunted.For example.the exponent weights.However.with lighter weight pairs.this for normal iudgments of linear extension is very bias may reverse to where they iudge the left side close to one.By contrast.neglect patients have to be heavier than the right.These results indicate diminished exponents,suggesting that they,unlike that crossover is a general perceptual phenomenon normal subjects,do not experience horizontal lines that is not restricted to the visual system. of increasing lengths as increasing proportionately It should be noted that these observations also mean that nonlinear transformations of the magnitude ofwith which they are confronted has been studied the most in the context of line bisection (Bisiach, Bulgarelli, Sterzi, & Vallar, 1983). Patients make larger errors on larger lines. Marshall and Halligan demonstrated that psychophysical laws could de￾scribe the systematic nature of these performances (Marshall & Halligan, 1990). Following this line of reasoning, Chatterjee showed that patients’ performances on line bisection, cancellation, single-word reading tasks, and weight judgments can be described mathematically by power functions (Chatterjee, 1995, 1998; Chatterjee et al., 1994a, 1992b; Chatterjee, Mennemeier, & Heilman, 1994b). In these functions, y = Kfb , f represents the objective magnitude of the stimuli, and y represents the subjective awareness of the patient. The constant K and exponent b are derived empirically. Power function relationships are observed widely in normal psychophysical judgments of magnitude estimates across different sensory stimuli (Stevens, 1970). An exponent of one suggests that mental rep￾resentations within a stimulus range are proportion￾ate to the physical range. Exponents less than one, which occur in the normal judgments of luminance magnitudes, suggest that mental representations are compressed in relation to the range of the physical stimulus. Exponents greater than one, as in judg￾ments of pain intensity, suggest that mental repre￾sentations are expanded in relation to the range of the physical stimulus. Chatterjee and colleagues showed that patients with neglect, across a variety of tasks, have power functions with exponents that are lower than those of normal patients. These observations suggest that while patients remain sensitive to changes in sensory magnitudes, their awareness of the size of these changes is blunted. For example, the exponent for normal judgments of linear extension is very close to one. By contrast, neglect patients have diminished exponents, suggesting that they, unlike normal subjects, do not experience horizontal lines of increasing lengths as increasing proportionately. It should be noted that these observations also mean that nonlinear transformations of the magnitude of sensations into mental representations occur within the central nervous system and not simply at the level of sensory receptors, as implied by Stevens (1972). Crossover in Neglect Halligan and Marshall (Halligan & Marshall, 1988; Marshall & Halligan, 1989) discovered that patients with neglect tended to bisect short lines to the left of the objective midpoint and seemed to de￾monstrate ipsilesional neglect with these stimuli. This crossover behavior is found in most patients (Chatterjee et al., 1994a) with neglect, and is not explained easily by most neglect theories. In fact, Bisiach referred to it as “a repressed pain in the neck for neglect theorists.” Using performance on single￾word reading tasks, Chatterjee (1995) showed that neglect patients sometimes confabulate letters to the left side of short words, and thus read them as longer than their objective length. He argued that this crossover behavior represents a contra￾lesional release of mental representations. This idea has been shown to be plausible in a formal computational model (Monaghan & Shillcock, 1998). The crossover in line bisection is also influenced by the context in which these lines are seen. Thus, patients are more likely to cross over and bisect to the left of the true midpoint if these bisections are preceded by a longer line (Marshall, Lazar, Krakauer, & Sharma, 1998). Recently, Chatterjee and colleagues (Chatterjee, Ricci, & Calhoun, 2000; Chatterjee & Thompson, 1998) showed that a crossoverlike phenomenon also occurs with weight judgments. Patients in general are likely to judge right-sided weights as heavier than left-sided weights. However, with lighter weight pairs, this bias may reverse to where they judge the left side to be heavier than the right. These results indicate that crossover is a general perceptual phenomenon that is not restricted to the visual system. Neglect 11