The present study aimed to examine whether the judgments of temporal order are made by the same "central processor" regardless of the characteristics of the sound stimuli. The influence of stimulus parameters (e.g., frequency, spectrum, duration, location) on auditory temporal order judgment (TOJ) thresholds was tested in seven groups with a total of 192 participants received two-tone sequences of different: frequencies (3 groups); spectrum widths, via a pure tone and a Gaussian noise burst (1 group); durations (2 groups); or locations, via asynchronous presentation to each ear (1 group). No difference in the mean rankings of TOJ thresholds was found for frequency, spectrum, and location parameters. TOJ thresholds for the duration condition, however, were significantly longer than for any of the other conditions. Notably, the threshold distributions for all the parameters (frequency, spectrum, duration, location) differed in shape. These findings raise the question as to whether we can rely upon the mean or median threshold as truly representative of TOJ threshold data. Furthermore, the data suggest that temporal order judgments for the different stimulus parameters are processed differently. The differences observed when analyzing the data with central tendency measures, as compared to analyzing the threshold distributions, may explain some of the mixed results reported in the literature on the mechanisms involved in temporal processing of different parameters. Stimulus parameters influence TOJ threshold distributions and response patterns, and may provide additional cues, beyond the standard temporal cue inherent in the TOJ procedure, by which participants may judge the order of the stimuli.
Transcranial direct current stimulation (tDCS) is a noninvasive tool to facilitate brain plasticity and enhance language abilities. Our study aims to search for a potential beneficial influence of tDCS on a cognitive linguistic task of naming which found to decline during aging. A group of fifteen healthy old adults [Formula: see text] were tested in naming 50 pictures of objects. Each subject participated in two sessions spanning on a one week period. One session included active tDCS stimulation and the other sham-placebo like stimulation. Subjects were blinded to stimulation type. During the active stimulation a bilateral protocol of anodal tDCS to the left Inferior Frontal Gyrus (IFG) combined with cathodal tDCS to the right IFG was delivered. Half of participants received active stimulation at the first session and sham at the second and half received the stimulations at the opposite order. Naming reaction time was measured at baseline, after active tDCS stimulation and after sham. 10 min of bilateral tDCS stimulation which was given after sham (training) was found to reduce naming reaction time among healthy adult subjects. These findings support the cooperative model (Weems and Reggia in Brain Lang 89:554-568, 2004) and point on strong interhemispheric connections during naming processing. It is also demonstrate the advantage of training to intensify the therapeutic effect of tDCS. Our results pinpoint on a potential tool to facilitate naming among aging people.
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