A comparison between a visual analogue scale and a four point scale as measures of conscious experience of motion

Can participants make use of the large number of response alternatives of visual analogue scales (VAS) when reporting their subjective experience of motion? In a new paradigm, participants adjusted a comparison according to random dot kinematograms with the direction of motion varying between 0° and 360°. After each discrimination response, they reported how clearly they experienced the global motion either using a VAS or a discrete scale with four scale steps. We observed that both scales were internally consistent and were used gradually. The visual analogue scale was more efficient in predicting discrimination error but this effect was mediated by longer report times and was no longer observed when the VAS was discretized into four bins. These observations are consistent with the interpretation that VAS and discrete scales are associated with a comparable degree of metacognitive sensitivity, although the VAS provides a greater amount of information.