Isoluminant stimuli in a familiar discrete keying sequence task can be ignored

Psychological Research https://doi.org/10.1007/s00426-019-01277-0 ORIGINAL ARTICLE Isoluminant stimuli in a familiar discrete keying sequence task can be ignored Willem B. Verwey1,2 Received: 13 May 2019 / Accepted: 2 December 2019 © The Author(s) 2019 Abstract Motor sequencing models suggest that when with extensive practice sequence representations have developed, stimuli indicating the individual sequence elements may no longer be used for sequence execution. However, it is not clear whether participants can at all refrain from processing these stimuli. Two experiments were performed in which participants practiced two 7-keypress sequences by responding to isoluminant key-specific stimuli. In the mixed condition of the ensuing test phase, the stimuli were displayed only occasionally, and the question was whether this would make participants stop processing these stimuli. In Experiment 1, the benefit of displaying stimuli was assessed after substantial practice, while Experiment 2 examined development of this benefit across practice. The results of Experiment 1 showed that participants rely a little less on these stimuli when they are displayed only occasionally, but Experiment 2 revealed that participants quickly developed high awareness, and that they ignored these stimuli already after limited practice. These findings confirm that participants can choose to ignore these isoluminant stimuli but tend to use them when they are displayed. These and other findings show in some detail how various cognitive systems interact to produce familiar keying sequences. Introduction The development of sequential movement skills is investigated with a variety of experimental procedures (for reviews, see, e.g., Abrahamse, Jiménez, Verwey, & Clegg, 2010; Doyon et al., 2009; Perruchet & Pacton, 2006; Rhodes, Bullock, Verwey, Averbeck, & Page, 2004; Rosenbaum, 2010; Verwey, Shea, & Wright, 2015). One of these procedures involves participants initially reacting to each of two fixed series of 2–7 successively presented key-specific stimuli in the so-called discrete sequence production (DSP) task (Abrahamse, Ruitenberg, De Kleine, & Verwey, 2013; Verwey, 1999). With practice, participants usually can perform the two sequences in response to just the first key-specific stimulus. This suggests that eventually they may ignore the stimuli after the first one. Still, there are reasons to assume * Willem B. Verwey 1 Faculty of Behavioral Sciences, Cognitive Psychology and Ergonomics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands 2 Human Performance Laboratories, Department of Health and Kinesiology, Texas A&M University, College Station, TX, USA that, if displayed, the use of key-specific stimuli may be mandatory. The present study therefore addressed whether participants stop processing key-specific stimuli when they are displayed only occasionally. I used isoluminant color changes as stimuli to explore this for the situation that stimulus display attracts little or no attention. Developing motor sequencing skill When participants practice discrete keying sequences, they begin by reacting to individual key-specific stimuli. However, the Cognitive framework for Sequential Motor Behavior (C-SMB) posits that already within tens of trials participants develop spatial and/or verbal central-symbolic sequence representations (Barnhoorn, Döhring, Van Asseldonk, & Verwey, 2016; Verwey, 2015; Verwey et al., 2015; for support from brain imaging studies, see Hikosaka et al., 1999; Verwey et al., 2019). Extracting individual responses from these spatial and verbal representations demands central-cognitive processing resources, and this makes sequence execution susceptible to interference by other cognitively loading tasks (Verwey, Abrahamse, & De Kleine, 2010; Verwey, Abrahamse, De Kleine, & Ruitenberg, 2014). After hundreds of trials, sequence representations develop in terms of motor parameters like activation patterns of 13 Vol.:(0123456789) Psychological Research agonist/antagonist muscles (Shea, Kovacs, & Panzer, 2011), musculoskeletal forces and dynamics (Krakauer, Ghilardi, & Ghez, 1999), joint angles (Criscimagna-Hemminger, Donchin, Gazzaniga, & Shadmehr, 2003), and/or posturerelated representations (Rosenbaum et al., 2009). These representations are denoted motor chunks (Broadbent, 1987; Graybiel, 1998; Sakai, Hikosaka, & Nakamura, 2004; Verwey, 1996). The use of motor chunks is characterized by effector-specific sequence learning (Verwey & Wright, 2004) and an overlap between successive movements (i.e., coarticulation; see, e.g., Gentner, Grudin, & Conway, 1980; Gonzalez-Sanchez, Dahl, Hatfield, & Godøy, 2019). Executing motor sequences based on motor chunks is fast because these representations code the sequences motorically and executing the individual responses demands few centralcognitive processing resources. The required cognitive processes merely involve preparing, selecting, and initiating motor chunks and no longer deriving response codes from sequence representations. Research demonstrated that when discrete keying sequences exceed about 4 or 5 responses, usually a relatively slow response develops that divides the sequence in segments of about 3 or 4 responses (Acuna et al., 2014; Verwey, 1999; Verwey & Eikelboom, 2003; Wymbs, Bassett, Mucha, Porter, & Grafton, 2012). These slow responses suggest that some dominant—central-symbolic or motor chunk—representation has a limited capacity and the slow response indicates the transition from one to the next sequence representation. The first response of the second and later segments is called a concatenation response; the other responses past the first one are execution responses (Abrahamse et al., 2013). According to C-SMB, the systems responsible for reacting to stimuli and for applying the central-symbolic and motor chunk representations are functionally separate systems that race to trigger each next response (Verwey, 2003; for other racing cognitive systems see Brown & Heathcote, 2008; Raab, 1962; Ratcliff, 2006; Ulrich & Miller, 1997). As these systems are stochastic and provide their output at times distributed around some average, a generally slower system may increase general execution rate because it occasionally still wins the race (Verwey, 2003). The contribution of key‑specific stimuli The development of sequence representations in a DSP task suggests that the contribution of the second and later keyspecific stimuli reduces with practice. Indeed, no longer displaying key-specific stimuli in a study with DSP sequences slowed individual responses by 155 ms after 144 practice trials per sequence (Verwey, Abrahamse, Ruitenberg, Jiménez, & De Kleine, 2011), and by only 32 ms after 720 practice trials (Ruitenberg, Verwey, Schutter, & Abrahamse, 2014). Sequencing models suggest that with even more practice the 13 stimulus–response (S–R) translation system may be entirely outrun by the sequenci (...truncated)