Dissociation between Reaction Time and Temporal Order Judgement
(Izabela Szumska, Tadeusz Kononowicz)
Simple reaction time
Since the beginning of mental chronometry studies a simple reaction time (RT) has been the most popular method. In this task participants are asked to press a button as fast as possible whenever they see a target. It has been repetitively demonstrated that RT decreases systematically as a function of increasing intensity.
Reaction Time can be divided into two separate components: perceptual latency and motor time - the time needed to activate the muscles and execute an action. However, changes in Reaction Time (e.g. under different intensity conditions - example on the right) reflect changes in perceptual latency rather than motor preparation. A difference in RT of different intensity levels (ΔRT) of 0 suggests simultaneity.
Temporal order judgement
Perceptual latency can be also estimated by Temporal Order Judgment (TOJ) task. In this task two stimuli (e.g. flashes) of different properties are presented using various inter-stimulus intervals (ISI). Participants’ task is to indicate which stimulus appeared first. When two stimuli are presented with
different intensities, the onset of the stimuli needs to be manipulated to result in a perceived simultaneity. The onset difference is typically referred to as the point of subjective simultaneity (PSS).
Dissociation between RT and TOJ task
Based on the assumption of common perceptual processes underlying TOJ and RT, these two methods should give the same results. However, it has been shown that results from these two tasks are remarkably different (e.g., Jaśkowski, 1999) with larger differences for ΔRT than in PSS. Different theories have been proposed to explain this dissociation. Accumulation models assume that only one feature of the internal response is taken into account in both tasks (Miller & Schwarz, 2006, Ulrich, 1988), while another approach assumes different features of the internal response are used for TOJ and RT tasks (Sternberg & Knoll, 1973), with RT based on a quick decision on incomplete data, and TOJ based on an evaluation of whole sensory stimulation. Most theoretical models assume that the incoming information is constant over time, that is, when stimuli are presented with constant light intensity. However, earlier work by Jaśkowski (1993) has suggested that an opposite dissociation (smaller differences in ΔRT than in PSS) can be obtained by manipulating the intensity rise times of visual stimuli.
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