Attention and stimulus characteristics determine the locus of motor- sequence encoding. A PET study

Hazeltine, Eliot · 1997 · Brain

DOI: 10.1093/brain/120.1.123

archive: archived pipeline: cataloged verified

Get this paper ↗ (DOI — opens at the source; we link to it, we don't host it)

Summary

This study investigates how stimulus characteristics and attentional constraints influence the neural substrates of motor-sequence learning. Building on previous research distinguishing between explicit and implicit memory systems, the authors sought to determine if the brain regions involved in learning sequences depend on whether stimuli are defined by spatial position or color, and whether attentional load alters these neural loci. The study utilized Positron Emission Tomography (PET) to measure regional cerebral blood flow (rCBF) in 11 right-handed subjects performing a serial reaction time (SRT) task. The experimental design involved two conditions: a dual-task condition where subjects performed a distracting tone-counting task to prevent explicit awareness of the sequence, and a single-task condition where subjects focused solely on the motor task, allowing for potential explicit learning. Crucially, the stimuli were color-coded circles presented at a central fixation point, rather than spatially separated lights used in prior studies. This manipulation removed the spatial component of the stimuli while maintaining the same motor responses. Subjects performed blocks of random and sequential trials, with PET scans acquired during sequence learning phases. Statistical analysis identified linear increases in rCBF correlated with performance improvements. Results demonstrated that learning occurred in both conditions, evidenced by increased reaction times when switching from sequence to random blocks. Under dual-task conditions, where learning was implicit, metabolic increases were observed in the left motor cortex, supplementary motor area, and putamen. These findings mirrored those of previous studies using spatial stimuli, suggesting that implicit motor-sequence encoding relies on similar motor-control regions regardless of stimulus type. However, under single-task conditions, where seven of eleven subjects became explicitly aware of the sequence, activation shifted to the right hemisphere, specifically involving the right prefrontal cortex, premotor cortex, and temporal lobe. Notably, explicit learning with color stimuli activated more ventral regions compared to the dorsal regions activated by spatial stimuli in prior work. The study concludes that the neural systems supporting motor-sequence learning are contingent on both stimulus properties and attentional constraints. While implicit learning engages consistent motor-related structures, explicit learning recruits prefrontal and temporal regions associated with working memory and recognition. The shift from dorsal to ventral activation when switching from spatial to color stimuli supports the hypothesis that working memory networks are task-dependent, varying according to the specific perceptual features being encoded. This provides evidence for dissociable neural mechanisms underlying explicit and implicit forms of sequence learning.

Key finding

The neural loci of motor-sequence learning shift depending on whether learning is implicit or explicit and whether stimuli are spatial or color-coded, with implicit learning engaging motor areas and explicit learning engaging prefrontal and temporal regions.

Methodology

lab_experiment

Sample size: 11

Provenance

The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed. Discovered via author_sweep_intake on 2026-05-28.

Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• automaticity skill acquisition