Fig 1.
Trial sequence of the fMRI task and behavioral performance.
A. For the data analyzed in the current study, participants remembered either one or three orientations. Sample stimuli were presented on the screen for 4 seconds, followed by a brief mask period of 0.25 seconds. After a delay of 7.75 seconds, participants rotated the needle of the response wheel to indicate the remembered orientation at the probed location. B. The raw response distribution of 1O and 3O trials, indicated by the gray histograms. The black lines indicate the envelope of target distribution, and pink and green lines indicate the envelope of response distribution, for 1O and 3O trials separately. C. Model-free and model-based behavioral performance. From left to right panel shows mean error, diffusion from the DOM model, drift from the DDM model, and diffusion from the DDM model. Error bars indicate ± 1 SEM. Data are available at osf.io/ajq3z. 1O, 1 orientation; 3O, 3 different orientations; DDM, drift–diffusion model; DOM, diffusion-only model; fMRI, functional magnetic resonance imaging.
Fig 2.
BOLD activity and brain-behavior correlations in IPS and PFC.
A. Trial-averaged BOLD activity in the IPS functional ROI. B. Time course of BOLD activity in the PFC functional ROI. Pink and green lines correspond to the 1O and 3O conditions, respectively. Error bars indicate ± 1 SEM. C. Within-subject correlations between behavioral parameter from DDM (drift and diffusion plotted separately) and IPS BOLD activity, at “late delay” time point (12 s). D. within-subject correlations between behavioral parameter (drift or diffusion) and PFC BOLD activity. In each plot, data from each subject are plotted in a different color, and the “1” and “3” symbols correspond to values from 1O and 3O trials, respectively. Lines illustrate the best fit of the group-level linear trend (i.e., the within-subject correlation) in relation to individual subject data. Data are available at osf.io/ajq3z. 1O, 1 orientation; 3O, 3 different orientations; BOLD, blood oxygen level–dependent; IPS, intraparietal sulcus; PFC, prefrontal cortex; ROI, region of interest.
Table 1.
Comparison between different regression models.
Fig 3.
Whole-brain regression analysis with drift and diffusion and ROI-based results in LO.
A. Whole-brain regression with drift and diffusion. Green denotes voxels showing load-dependent BOLD activity that can be better explained by load-dependent changes in drift, and red denotes voxels showing load-dependent BOLD activity that can be better explained by load-dependent changes in diffusion. For visualization purposes, results were clusterized at a threshold of 20 voxels. The left 2 panels show results from the left hemisphere, and the right 2 panels show results from the right hemisphere. The significance of the regression models was corrected using the FDR method at p < 0.05. B. Trial-averaged BOLD activity in the LO1 anatomical ROI. C. Time course of BOLD activity in the LO2 anatomical ROI. Pink and green lines correspond to the 1O and 3O conditions, respectively. Error bars indicate ± 1 SEM. D. Within-subject correlations between behavioral parameter from DDM (drift and diffusion plotted separately) and LO1 BOLD activity, at “late delay” time point (12 seconds). E. within-subject correlations between behavioral parameter (drift or diffusion) and LO2 BOLD activity. In each plot, data from each subject are plotted in a different color, and the “1” and “3” symbols correspond to values from 1O and 3O trials, respectively. Lines illustrate the best fit of the group-level linear trend (i.e., the within-subject correlation) in relation to individual subject data. Data are available at osf.io/ajq3z. 1O, 1 orientation; 3O, 3 different orientations; BOLD, blood oxygen level–dependent; FDR, false discovery rate; LO, lateral occipital cortex; ROI, region of interest.