Mental Chronometry: Do Imagined Times Merely Relate to Task Duration?

Prolonged movement time as a function of task difficulty (as defined by the Index of Difficulty [ID]) can be equally prevalent within executed and imagined movements ─ something referred to as the mental chronometry effect. This effect has been leveraged as support for functional equivalence, where an internal representation can be shared for execution and imagery. However, times tend to rise exponentially more for imagined, compared to executed, movements, which could be attributed to the time spent within a task. Fifteen participants attempted execution and imagery of a reciprocal aiming movement between two targets that assumed different levels of ID (4, 5, 6 bits). They did this either over 3 or 5 cycles of movement to generate short- and long-duration movements, respectively. Mean times and time-ID slope/gradient coefficients revealed that the time within imagery was generally no longer than execution. However, the rise in time as a function of ID tended to be even greater when undertaking 3 compared to 5 cycles within imagery, but not execution. Overall, these findings may counter the suggestion that time spent within imagery is positively related to duration. However, further research is perhaps warranted to help formulate broader recommendations for imagery across different durations.