Why free choices take longer than forced choices: evidence from response threshold manipulations.

Response times (RTs) for free choice tasks are usually longer than those for forced choice tasks. We examined the cause for this difference in a study with intermixed free and forced choice trials, and adopted the rationale of sequential sampling frameworks to test two alternative accounts: Longer RTs in free choices are caused (1) by lower rates of information accumulation, or (2) by additional cognitive processes that delay the start of information accumulation. In three experiments, we made these accounts empirically discriminable by manipulating decision thresholds via the frequency of catch trials (Exp. 1) or via inducing time pressure (Exp. 2 and 3). Our results supported the second account, suggesting a temporal delay of information accumulation in free choice tasks, while the accumulation rate remains comparable. We propose that response choice in both tasks relies on information accumulation towards a specific goal. While in forced choice tasks, this goal is externally determined by the stimulus, in free choice tasks, it needs to be generated internally, which requires additional time.