Dissociating premotor and motor components of response times: Evidence of independent decisional effects during motor-response execution

Psychonomic Bulletin & Review https://doi.org/10.3758/s13423-025-02663-z BRIEF REPORT Dissociating premotor and motor components of response times: Evidence of independent decisional effects during motor‑response execution Saman Kamari Songhorabadi1 · Simone Sulpizio2,3 · Michele Scaltritti1 Accepted: 3 February 2025 © The Author(s) 2025 Abstract Traditional measures of response times (RTs) capture the summed duration of multiple latent and overt processes, including motor-response execution. The present research assessed the functional independence of the decisional components unfolding before vs after the onset of the muscular activation in the context of a lexical decision task requiring manual button-press responses. Specifically, the lexicality effect (slower latencies for nonwords compared to words) was separately tracked across premotor and motor components of RTs under different regimes of decision bias. Whereas at the premotor level the lexicality effect was modulated by the proportion of word vs nonword trials in the block, with a reversal of the lexicality phenomenon when nonwords occurred in 75% of the trials, motor times (i.e., a chronometric measure of response duration) consistently displayed longer durations for nonword responses, irrespective of bias manipulation. The results point to a partial functional independence between the decisional components involved at the premotor vs motor level, suggesting that the onset of motor behavior may represent the onset of specific decisional processes, rather than the termination or the continuation of computations unfolding in the premotor interval. Keyword Mental chronometry; response time; decision making; motor-response execution Introduction The research was funded by the European Union–Next Generation EU – PRIN 2022 PNRR (DD 1409, 14/09/22) – PNRR – M4 – C2 – INV1.1 – PRIN – Project Title [Functional characterization of decisional components in motor responses for young and older adults] – Grant Number [P2022C39ZH] – CUP [E53D23019540001]. We are grateful to Margherita Cardellini for her help during data collection. * Michele Scaltritti 1 Dipartimento Di Psicologia e Scienze Cognitive, Università Degli Studi Di Trento, Corso Bettini 31, 38068 Rovereto, TN, Italy 2 Dipartimento Di Psicologia, Università Degli Studi Di Milano-Bicocca, Milan, Italy 3 Milan Center for Neuroscience (Neuromi), Università Degli Studi Di Milano-Bicocca, Milan, Italy Mental chronometry, one of the earliest breakthroughs for modern psychological sciences, builds on the notion that response time (RT) captures the duration of the multiple processes involved in a task (e.g., Luce, 1986; Posner, 1978), including the motor-activity required to perform the overt response. In case of discrete behavioral responses typically used in psychological experiments (e.g., button-press), RTs can in fact be divided into a premotor time (PMT), extending from stimulus onset to the initiation of motor activity, and a motor time (MT), extending from the onset of motor activity until the completion of the response (Botwinick & Thompson, 1966; Weiss, 1965). The functional characterization of the MT, as well as its functional relationship with PMT, remain contentious to this day. Traditionally, the onset of motor behavior has been considered the endpoint of upstream cognitive computations and the beginning of motor-response execution, envisaged as a separate stage within serial architectures (e.g., McClelland, 1979; Ratcliff, 1978; Sternberg, 1969). Under this perspective, PMTs and MTs can be mapped onto independent Vol.:(0123456789) Psychonomic Bulletin & Review categories of processes represented, respectively, by central cognitive vs peripheral motor computations. This view has been challenged by different lines of evidence. Pioneering research has highlighted online processes of response control operating during the unfolding of the motor-response itself (e.g., Allain et al., 2004; Burle et al., 2002; Fluchère et al., 2018; Hasbroucq et al., 1999; Ramdani et al., 2013, 2021; Roger et al., 2014), mainly through inhibitory and corrective mechanisms on muscular activations. Minimally, motor-response execution is thus shaped by monitoring processes related to executive and cognitive control. In addition, results from perceptual decision-making tasks indicate that the amount of sensory evidence exerts a reliable influence on both PMTs and MTs (Dendauw et al., 2024; Servant et al., 2021; Weindel et al., 2021), pointing to the accumulation of a decision variable that propagates beyond response onset and informs motor-response execution (e.g., Calderon et al., 2018; Dendauw et al., 2024; Eriksen & Schultz, 1979; Verdonck et al., 2021). Under this perspective, the cognitive characterization of MTs is largely inherited from PMTs, with the two intervals being shaped by the same cognitive/decisional factor(s) that continuously unfold over both components. A further set of findings, however, seems to expand the hypothesis space by pointing to a differentiation in the decisional phenomena that modulate premotor vs. motor intervals, and consequently in the underlying decisional components. First, not all decision-related manipulations propagate their influence from PMT to MT (Weindel et al., 2021), as one would expect under the assumption of a single decisional variable informing both intervals. In particular, studies focusing on the visual lexical decision paradigm, in which participants categorize strings of letters as real words (e.g., house) vs nonwords (e.g., flirp), have shown that while the lexicality effect (slower RTs for nonwords compared to words) reliably affect both PMTs and MTs, the word frequency effect remains bounded to PMTs (Scaltritti et al., 2023; but see Dendauw et al., 2024). Second, different decision-related phenomena, when jointly manipulated, can combine in different ways across PMTs and MTs. Specifically, lexicality and speed-accuracy tradeoff (SAT) manipulations in lexical decision display interactive effects at the level of PMTs, but additive effects on MTs, with the difference between words and nonwords remaining constant in terms of execution times, irrespectively of the SAT regime (Scaltritti et al., 2024). Taken together, these findings suggest that, although motor-response execution is permeable to multiple cognitive factors, it may not merely reflect the same dynamics observed during PMTs. The last line of evidence comes from the comparison between correct vs incorrect responses in binary decision tasks, in which error trials display faster PMTs, but slower MTs, compared to correct responses (e.g., Allain et al., 2004; Rochet et al., 2014; Smigasiewicz et al., 2020; Weindel et al., 2021). This peculiar pattern has been mostly related with online response control mechanisms, which would try to inhibit incorrect responses during their unfolding. Importantly, it suggests that PMTs an MTs are empirically dissociable, b (...truncated)