the independent variable. Due to the binary nature of the response, the data were analyzed using Somers’ d. This is a test of association between the outcome (frequency of correct responses) and the ordinal independent varia- ble (eccentricity; see Siegel & Castellan, 1988). To evaluate the ability to detect dual targets compared to single targets, the data were transformed into an extinction index derived from that of Duncan et al. (1999). An index was calculated separately for LH, CM, and RH configurations by dividing the proportion of correct responses on dual-target trials (PD) by the prod- uct of the proportion of correct responses for the single trials (PS) at the corresponding two locations: PD/ (PSleft × PSright); see Table 2. An index value equal to unity represents equivalent performance on both single- and dual-target trials, whilst an index value of less than unity reflects relatively worse performance on dual-target trials. To measure the degree of association between each patient’s visual and auditory extinction indices, stimulus modality only was permuted across all locations. Ran- dom permutations were repeated 1,000,000 times in order to estimate an empirical distribution for any differences in the index under the hypothesis. Reported p-values estimate the two-tailed probability that there is no differ- ence in the distribution of visual and auditory indices over the three spatial configurations. Randomization tests were also used to compare the patients’ extinction indices with the observed indices for the control group. In this comparison the p-value reflects the two-tailed proba- bility that the patient’s performance is consistent with that of the controls (see Figure 3). Analyses: TOJ The number of correctly named targets at each SOA was recoded to represent the proportion of “right-first” responses. These data were then analyzed using a probit analysis (Finney, 1964), which produces a probability estimate for each participant of right-first responses as a linear function of SOA, transformed via a cumulative NEGLECT IN VISION AND AUDITION 75 standard normal distribution (McCullagh & Nelder, 1983). The resulting probability functions were then used to estimate each participant’s point of subjective simul- taneity (PSS): the point at which right-first and left-first decisions are equally probable (i.e., .5). PSS values devi- ating from zero reflect slowed responses for the ipsile- sional (PSS > 0) or contralesional stimulus (PSS < 0). Goodness-of-fit estimates (GoF) for the observed and estimated data for each individual were calculated using the deviance statistic (p-values < .05 suggest that the psychometric function is a poor fit). For one case (J.B. auditory test), a single incorrect response at SOA of 300 ms was omitted as an outlier on the basis that it was grossly inconsistent with performance at adjacent SOAs and reduced the GoF. The deviance statistic and the 95% confidence intervals around the PSS were calculated using Matlab’s “glmfit” routine (Version 7.5.0; Math- Works Inc., 2007; see Collett, 2002, for a description). For each individual, the sharpness of temporal acuity was also estimated using the just noticeable difference (JND). This is calculated as half of the SOA between the point on the probit function at which 25% and 75% of targets were reported as right-first trials (Shore & Spence, 2005). Table 3 reports the statistics associated with the individual probit analyses for each patient. RESULTS Controls Controls performed near ceiling on both extinction tasks, and there was no significant effect of eccentricity (α = .05). For visual stimuli, mean target accuracy was 99% (SD = 0.9%) for single targets and 99% (SD = 0.6%) for dual targets. For auditory stimuli, mean accuracy was 99% (SD = 1.0%) for single targets and 99% (SD = 0.3%) for dual targets (see Table 2). Mean extinction indices for stimuli at the LH, CM, and RH spatial con- figurations approached unity in the visual and auditory TABLE 2 Proportion of trials correctly identified as single- and dual-target displays and extinction indices Control F.D. J. B. S D EI S D EI S D EI LH 1.0 .99 1.00 .92 .20 0.24*** 1.0 1.0 1.0 Visual CM .98 .99 1.03 1.0 .50 0.5*** 1.0 1.0 1.0 RH .99 1.0 1.00 1.0 1.0 1.0 1.0 1.0 1.0 LH .99 .99 1.02 1.0 .13 0.13*** 1.0 .90 0.9 Auditory CM 1.0 .99 1.01 .92 .33 0.3*** 1.0 .80 0.8** RH .99 .99 1.01 .92 .66 0.72*** 1.0 1.0 1.0 Note. S = single-target display; D = dual-target display; EI = extinction index. Single-target scores are reported across the two locations in each spatial configuration. Mean proportion correct scores are reported for controls. LH = left hemispace, CM = central meridian, and RH = right hemispace. **.001 < p < .01; ***p < .001.