When Timing the Mind One Should Also Mind the Timing: Biases in the Measurement of Voluntary Actions

Cortical Movement Preparation and Conscious Decisions: Averaging Artifacts and Timing Biases

“…Although the potential biases suggested by Joordens et al (2002) do not seriously compromise our third conclusion and actually strengthen our fourth conclusion, we comment further on several of the points that they raised. First, consider the suggestion that there was decision bias.…”

“…If the representational momentum effect were large, one would expect all timing judgments to be too late with this clock task, but clearly they are not. We note too that Joordens et al (2002) did not attempt to provide any specific evidence for an effect of representational momentum within their experiment.…”

“…On at least one story about what happens in the standard task, though, we think that the simple RT task should be embedded, as Joordens et al (2002) have done but others have not. Specifically, imagine that a participant in the standard task generates a spontaneous movement by monitoring for some random internal timing signal to be generated.…”

“…And this source of bias merely strengthens the fourth conclusion, as noted by van de Grind (2002), because if the true conscious decisions are even earlier than our measurements indicated them to be then they precede LRP onset by an even greater amount. Joordens et al (2002) identified two further sources of potential bias in participants' reports of their decision times: (a) a memory bias due to a representational momentum effect and (b) a decision bias due to a higher proportion of ''after'' than ''before'' trials. The memory bias would have been present in all experiments using the clock-based measurement of decision times, but the decision bias may have been specific to the particular psychophysical tracking procedure that we used to adjust the location of the test spot on the clock face.…”

“…A closer look at the procedure used by Joordens et al (2002) suggests that, although they did not discuss it as such, they may have identified a third possible source of bias in the clock task that has not been considered elsewhere. Participants in their task watched a moving clock display, as usual.…”