Academic journal article Canadian Journal of Experimental Psychology

Modulating the Interference Effect in Timing with Varying Stimulus Onset Asynchrony

Academic journal article Canadian Journal of Experimental Psychology

Modulating the Interference Effect in Timing with Varying Stimulus Onset Asynchrony

Article excerpt

The interference effect on time judgments, when subjects are also required to perform a concurrent nontemporal task, is one of the most reliable findings in the time perception literature. In the present study, the interference between a time discrimination task (short or long tone) and a digit classification task (even or odd digit) was analysed using the overlapping tasks paradigm. Reaction times in the digit task were shorter at longer values of stimulus onset asynchrony (SOA) in Experiment 1, showing a clear modulation of interference with varying the relative position of the tasks. Using longer tone durations in Experiment 2, reaction times in the digit task were affected not only by the overlap between the tasks but also by the temporal proximity of responses in the timing and digit tasks. In Experiment 3, the effect of varying the SOA on performance on the digit task was abolished when the auditory tone was irrelevant, thus eliminating an interpretation in terms of distraction from the tone offset. We conclude that the interference effect in concurrent time discrimination and digit classification may be modulated by the degree of overlap between the tasks as well as by the overlap between late processing stages related to decision and response components in the 2 tasks.

Keywords: time discrimination, timing, interference effect, dual-task paradigm, stimulus onset asynchrony

The interference effect is one of the most consistent findings in the human timing literature (Brown, 1997, 2008, 2010). It generally refers to a shortening of perceived time when it is estimated while performing some attention-demanding task relative to conditions in which timing is performed alone. For example, a 2-s tone may be judged as lasting about 2 s if the judgment is made under single-task timing conditions, but it may be judged as lasting about 1.5 s if a change in tone frequency must be detected during the temporal judgment task (e.g., Casini & Macar, 1997). The shortening is usually greater as demands in concurrent processing increase, an effect observed with a wide range of concurrent tasks involving perceptual (Casini & Macar, 1997; Champagne & Fortin, 2008; Field & Groeger, 2004), motor (Brown & Bennett, 2002), and cognitive (Fortin, Champagne, & Poirier, 2007; Fortin, Schweickert, Gaudreault, & Viau-Quesnel, 2010; Neath & Fortin, 2005; Rammsayer & Ulrich, 2005; Zakay, 1993) processing. These results are classically observed in prospective timing tasks, when participants know in advance that temporal judgments are required.

The interference effect is usually explained by an interruption in accumulation of temporal information. This interpretation is common to accumulator models of time estimation such as the scalar expectancy theory (SET; Gibbon, 1977) and its associated information-processing models (Church, 1984; Gibbon, Church, & Meek, 1984; see also Creelman, 1962; Treisman, 1963), as well as in the attentional gate model (Zakay & Block, 1996). According to this interpretation, the basis of temporal judgments is an accumulation of temporal information (defined as units or pulses) emitted by an internal source of temporal information. For example, in a serial temporal production task, participants are asked to press on one key of the computer keyboard at a rate of one press every 5 s. At each keypress, participants must start estimating time and press again on the key when they judge that 5 s have elapsed since meir previous press. According to SET, the participants start accumulating pulses emitted from an internal source of temporal information, an "internal clock." Pulses are accumulated and stored in an accumulator/counter until the accumulated count is close enough to the number of pulses corresponding to the 5-s critical duration. A keypress is executed as soon as the criterion number of pulses is reached.

In SET, deciding whether or not the criterion number of pulses is reached at a particular instant, during a timing task, is based on a comparison process between the current number of pulses in the accumulator/counter with a criterion number in reference memory. …

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