Abstract
One of the critical factors that guide choice behavior is the prior bias of the decision-maker with respect to different options, namely, the relative readiness by which the decision-maker opts for a specific choice. Although previous neuroimaging work has shown decision bias related activity in the orbitofrontal cortex, intraparietal sulcus (IPS) and dorsolateral prefrontal cortex, in a recent work by Javadi et al. (2015), primary motor cortex was also implicated. By applying transcranial direct current stimulation (tDCS), they have revealed a causal role of the primary motor cortex excitability in the induction of response time (RT) differences and decision bias in the form of choice probability. The current study aimed to replicate these recent findings with an experimental design that contained a sham group to increase experimental control and an additional testing phase to investigate the possible after-effects of tDCS. The conventional decision outputs such as choice proportion and RT were analyzed along with the theory-driven estimates of choice bias and non-decision related components of RTs (e.g., motor implementation speed of choices made). None of the statistical comparisons favored the alternative hypotheses over the null hypotheses. Consequently, previous findings regarding the effect of primary motor cortex excitability on choice bias and response times could not be replicated with a more controlled experimental design that is recommended for tDCS studies (Horvath et al., 2015). This empirical discrepancy between the two studies adds to the evidence demonstrating inconsistent effects of tDCS in establishing causal relationships between cortical excitability and motor behavior.
Highlights
Many of our routine decisions include relatively speedy judgments made based on a continuous stream of sensory information
The participants completed over 2200 trials each, missed the 800 ms response deadline in 3.9% of the trials, and responded to 48.6% of the trials with their left hand across all conditions
To assess whether we could successfully replicate the first experiment of Javadi et al (2015), we conducted the statistical analyses reported in that study on a subset of our data that corresponded to their dataset
Summary
Many of our routine decisions include relatively speedy judgments made based on a continuous stream of sensory information. These range from deciding if we have previously met a given person to deciding if an approaching cab is occupied or not. Motor tDCS and Decision Making (or more) decision states it favors In laboratory settings, these decisions are generally investigated via two-alternative forced choice (2AFC) tasks. We used transcranial direct current stimulation (tDCS) as a tool to investigate the potential causal roles of primary motor cortex activity in the modulation of such latent variables in a perceptual decision making task
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