Temporal order judgments activate temporal parietal junction

Abstract

Perceptual temporal order judgments require an individual to determine the relative timing of two spatially separate events. Here we reveal the brain regions involved with this task. We had participants observe perceptually identical visual stimuli while conducting two different tasks: discriminating temporal order or discriminating spatial properties. By contrasting the functional magnetic resonance imaging signals during these tasks, we were able to isolate regions specifically engaged by each task. Participants observed two briefly presented rectangles. In one task, participants were instructed to report which appeared first, and, in the other, they were requested to report which rectangle was squarer. A potential confound of this study is that the temporal order judgment (TOJ) task required processing of brief events (onsets), whereas the shape task did not require temporal selectivity. To address this, we conducted a second study in which both tasks required discriminating brief events concurrent with the object onsets. The stimuli were similar to the first experiment, except a gray line was briefly superimposed on each rectangle at onset. Participants reported either which rectangle appeared first (TOJ) or which rectangle had a slightly wider gray line (shape). The first study found that the TOJ task resulted in greater bilateral activation of the temporal parietal junction (TPJ). The second revealed TOJ activation in the TPJ of the left hemisphere. This suggests that TPJ activation increases when we need to temporally sequence information. This finding supports the notion that the TPJ may be a crucial component of the "when" pathway.

Figure 1.

A visual representation of the stimuli presented in the order of their presentation in each experiment. Top, Experiment 1. A fixation is followed by the presentation of the first rectangle (here red), which can appear in any one of the four corners. This is followed by the presentation of a second (here slightly taller) rectangle (green) that appears in the opposite corner. The size, onset, and location of the two rectangles presented in each trial were randomized. In this example, the fixation mark is yellow, noting that the participant should report which item appeared first (TOJ); trials with a blue fixation prompted the reporting of which rectangle was more square (shape). Bottom, Experiment 2. Identical except that the rectangles are the same shape and initially have gray lines in them of differing widths. In this experiment, the shape discrimination was based on these brief gray bars. Importantly, the durations of the shape and TOJ tasks in experiment 2 were equivalent.

Figure 2.

Brain renderings and axial slices displaying the Z-scores of clusters of fMRI voxels more significantly activated by the TOJ than shape tasks for experiment 1 (blue to gray to white gradient) and experiment 2 (red to yellow to white gradient). Top left, Sagittal rendering of the left hemisphere. Top middle, Rendering from a superior–posterior viewpoint. Top right, Sagittal rendering of the right hemisphere. Brain slices are axial and displayed on a template created by averaging the brains of the 12 participants from experiment 2. They are presented under their MNI coordinates (blue text), and a sagittal slice is included with blue lines, indicating the positions of each axial slice. All Z-scores presented are >2.3 and have survived a corrected cluster threshold (p < 0.05).

Figure 3.

Brain renderings and axial slices displaying the Z-scores of clusters of fMRI voxels more significantly activated by TOJ task than baseline (gradient of dark gold to light gold corresponding to Z-scores of 0–8) and shape task more than baseline (gradient of dark cyan to light cyan corresponding to Z-scores of 0–8). Left, Results from experiment 1. Right, Results from experiment 2. Top, Rendering from a superior–posterior viewpoint. Bottom, Axial slices displaying the activation maps. Slices are displayed on a template created by averaging the brains of the 12 participants from each corresponding experiment (with slice coordinates shown as blue text, and blue lines on the sagittal slice illustrating slice positioning). All Z-scores presented are >2.3 and have survived a corrected cluster threshold (p < 0.05).