Stimulus-Onset-Asynchrony as the Main Cue in Temporal Order Judgment

Elderly individuals often complain of difficulties in understanding speech, especially when heard against a background noise or when there are multiple speakers. One of the hypothesized reasons for these complaints is the reported age-related decline in auditory temporal processing (Schneider & Pichora-Fuller, 2001; Schneider, Daneman, & PichoraFuller, 2002). The rationale underlying this hypothesis is that the appropriate use of speech cues relies on several types of auditory temporal resolution, which research has shown is age-related (Gordon-Salant, 2005; Pichora-Fuller & Souza, 2003; Schneider & Pichora-Fuller, 2001; Schneider et al., 2002). A large number of studies have compared young and elderly subjects on a variety of auditory temporal resolution tasks and reported poorer resolution by the elderly as compared to the younger individuals. Elderly adults perform poorer than younger adults in gap detection tasks and need longer silent intervals to identify the presence of a gap when the marker signal is 250 msec or shorter (Fink, Churan, & Wittmann, 2005; Fitzgibbons & Gordon-Salant, 2001; Grose, Hall, & Buss, 2006; Lister & Roberts, 2005; Lister & Tarver, 2004; Roberts & Lister, 2004; Schneider & Hamstra, 1999; Schneider, Speranza, & Pichora-Fuller, 1998; Snell, 1997; Snell & Frisina, 2000; Snell, Mapes, Hickman, & Frisina, 2002; Strouse, Ashmead, Ohde, & Grantham, 1998). Other studies have reported that older subjects have difficulty in correctly identifying temporal order in a tonal sequence (Fitzgibbons & Gordon-Salant, 1998; Gordon-Salant & Fitzgibons, 1999). Furthermore, a number of studies have reported that older individuals require larger differences in duration between two tones in order to detect a difference (Abel and Hay, 1996; Fitzgibbons & GordonSalant, 1994, 1995, 1996). Similar results, indicating poorer discrimination by the elderly, were found when comparing older and younger adults on binaural temporal processing tasks such as locating a tone in the frontback plane (Abel and Hay, 1996), tone localization (Abel, Giguère, Consoli, & Papsin, 2000) and click lateralization (Babkoff, Muchnik, Ben-David, Furst, Even-Zohar, & Hildesheimer, 2002; Strouse et al., 1998). Traditionally, most of the studies of age-related decline in temporal resolution have used the gap detection task, in which the duration of the silent interval within a tone is manipulated until the participant (young or elderly adult) is able to detect a non-continuous tone (Ezzatian , PichoraFuller , & Schneider, 2010; Fink et al., 2005; Fitzgibbons & Gordon-Salant, 2001; Grose, Hall, & Buss, 2006; Lister & Roberts, 2005; Lister & Tarver, 2004; Roberts & Lister, 2004). Other researchers have used the duration discrimination task, in which the duration of a tone is manipulated and changes in duration are detected (Abel and Hay, 1996; Gordon-Salant & Fitzgibbons, 1999; Fitzgibbons & Gordon-Salant, 1994, 1995). Taken together, the results of these studies have shown that the elderly require larger gaps and longer tone durations than the young adults to attain the same levels of discrimination. In general, the common feature in these and other tasks that were used to measure temporal resolution is that the discrimination may be accomplished by one ear only. Consequently, the temporal cue may not necessarily be central, although some evidence points to the involvement of higher order processes in the temporal range associated with gap detection (Ross, Schneider, Snyder, & Alain, 2010). In our studies we have used a different method for studying auditory temporal resolution among the elderly, and other populations of interest, the dichotic temporal order judgment (TOJ) task. This task involves the identification of the order of two sounds that are equal in frequency and intensity (Ben-Artzi, Fostick & Babkoff, 2005; Babkoff, Zukerman, Fostick, & Ben-Artzi, 2005). The tones are delivered to each ear and are separated by a range of inter-stimulus intervals (ISI). The listener is required to judge the order of presentation of the tones to the two ears (left-right or rightleft). This paradigm eliminates the possible use of spectral cues for order judgment and depends on central mechanism(s) for the temporal resolution of information received from both ears. The elimination of spectral cues reinforces the conclusion that the judgment is based on the temporal domain. Two temporal parameters are manipulated when a tone is presented to each ear separated by an inter-stimulus interval: i) the silent interval (i.e., the inter-stimulus interval); and ii) the stimulus onset asynchrony (SOA) (i.e., the time from the onset of the tone to the first ear and the onset of the tone to the second ear. The contribution of each of the two parameters to performance level can be studied by manipulating tone duration, while keeping ISI constant. The main purpose of the current study was to identify the temporal parameter that explains most of the variance associated with the judgment of temporal order.