Elderly listeners are known to differ considerably in their ability to understand speech in noise. Several studies have addressed the underlying factors that contribute to these differences. These factors include audibility, and age-related changes in supra-threshold auditory processing abilities, and it has been suggested that differences in cognitive abilities may also be important. The objective of this study was to investigate associations between performance in cognitive tasks and speech recognition under different listening conditions in older adults with either age appropriate hearing or hearing-impairment. To that end, speech recognition threshold (SRT) measurements were performed under several masking conditions that varied along the perceptual dimensions of dip listening, spatial separation, and informational masking. In addition, a neuropsychological test battery was administered, which included measures of verbal working and short-term memory, executive functioning, selective and divided attention, and lexical and semantic abilities. Age-matched groups of older adults with either age-appropriate hearing (ENH, n = 20) or aided hearing impairment (EHI, n = 21) participated. In repeated linear regression analyses, composite scores of cognitive test outcomes (evaluated using PCA) were included to predict SRTs. These associations were different for the two groups. When hearing thresholds were controlled for, composed cognitive factors were significantly associated with the SRTs for the ENH listeners. Whereas better lexical and semantic abilities were associated with lower (better) SRTs in this group, there was a negative association between attentional abilities and speech recognition in the presence of spatially separated speech-like maskers. For the EHI group, the pure-tone thresholds (averaged across 0.5, 1, 2, and 4 kHz) were significantly associated with the SRTs, despite the fact that all signals were amplified and therefore in principle audible.

Saccadic reaction time (SRT) to a visual target tends to be shorter when auditory stimuli are presented in close temporal and spatial proximity, even when subjects are instructed to ignore the auditory non-target (focused attention paradigm). Previous studies using pairs of visual and auditory stimuli differing in both azimuth and vertical position suggest that the amount of SRT facilitation decreases not with the physical but with the perceivable distance between visual target and auditory non-target. Steenken et al. (Brain Res 1220:150-156, 2008) presented an additional white-noise masker background of three seconds duration. Increasing the masker level had a diametrical effect on SRTs in spatially coincident versus disparate stimulus configurations: saccadic responses to coincident visual-auditory stimuli are slowed down, whereas saccadic responses to disparate stimuli are speeded up. Here we show that the time-window-of-integration model accounts for this observation by variation of a perceivable-distance parameter in the second stage of the model whose value does not depend on stimulus onset asynchrony between target and non-target.

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In the redundant-signals paradigm for simple reaction time (RT), the observer must initiate a response as quickly as possible following the detection of any stimulus onset. A typical finding is a redundancy gain: Responses are faster, on average, when two or more signals are presented simultaneously than when a single signal appears. This redundant-signals effect (RSE) has often, although not always, been replicated under different experimental settings-for example, comparing uni-versus multimodal stimulation (Diederich, 1995;Diederich & Colonius, 1987;Gielen, Schmidt, & Van den Heuvel, 1983;Miller, 1982Miller, , 1986Molholm, Ritter, Javitt, & Foxe, 2004), single versus multiple stimuli within the same modality (e.g., Schwarz & Ischebeck, 1994), or monocular versus binocular stimulation (Hughes & Townsend, 1998; Westendorf & Blake, 1988)-and for specific populations (see, e.g., Corballis, 1998;Miller, 2004;Reuter-Lorenz, Nozawa, Gazzaniga, & Hughes, 1995;and Savazzi & Marzi, 2004, all for split-brain individuals; and Marzi et al., 1996, for hemianopics).Raab (1962) proposed a race model for simple RT, postulating that (1) each individual stimulus elicits a (normally distributed) detection process performed in parallel to the others and (2) the winner's time determines the observable RT. The race model opens up the possibility that the RSE is generated by statistical facilitation: If detection latencies are interpreted as (nonnegative) random variables, the time to detect the first of several redundant signals is faster, on average, than the detection time for any single signal. Testing the race model amounts to probing whether an observed RT speedup is too large to be attributable to statistical facilitation (viz., probability summation), no matter which distributional assumptions have been made.A test of general race models was developed by Miller (1978Miller ( , 1982, showing thatmust hold for all t 0. This race model inequality (RMI) follows fromfor any pair of random variables (X, Y ) with a joint probability distribution based on Pr XY and with its marginal distributions identical to Pr X and Pr Y . Thus, as was observed in Luce (1986, p. 130), the RMI test requires that the RT distributions in the single-signal conditions are identical to the corresponding (marginal) RT distributions in the redundant-signals condition (cf. Colonius, 1990). Note that, for fixed t, Inequality 2 corresponds to the well-known Boole's inequality (e.g., Billingsley, 1979). Neglecting possible additional components (such as motor time), the inequality stipulates that the RT distribution function for redundant stimuli is never larger than the sum of the RT distributions for the single stimuli. A violation of this inequality is interpreted as an indication of an underlying coactivation mechanism or some other strong form of nonindependence. The race model inequality (RMI) introduced in Miller (1982) puts an upper limit on the amount of reaction time facilitation within the redundant-signals paradigm that is consistent with a race ...