The Journal of Neuroscience, March 29, 2006, ():
The Neural Site of Attention Matches the Spatial Scale of Perception
J. Neurosci. Hopf et al.
26: 3532
Supplemental data
Files in this Data Supplement:
- supplemental material -
Behavioural data. Supplemental Fig. 1a shows mean response times (RT) and accuracy (percent correct) for large- and small-scale targets in the left and right visual fields (LVF and RVF). Although, RTs were slightly longer for small-scale targets than for large-scale targets, this difference was only marginally significant in a two-way repeated measures analysis of variance with factors of target scale and visual field (F1,9 = 4.0, p = .076). There was also no significant effect of visual field (F1,9 = 4.0, p= .076) or significant scale x visual field interaction (F1,9 = 2.36, p = .16). Responses were also slightly less accurate for small-scale targets than for large-scale targets, especially in the RVF (Supplemental Fig. 1b). A corresponding ANOVA of the accuracy data yielded a significant interaction between target scale and visual field (F1,9=14.7, p<.05), along with marginally significant main effects of scale (F1,9=4.29,p=0.068) and visual field (F1,9=4.04, p=0.075). Thus, the small-scale targets were slightly more difficulty to identify than the large scale targets, especially in the right visual field.
- supplemental material -
Eye movements. Supplemental Fig. 2a shows the grand average HEOG waveform after artifact rejection from the main ERP/ERMF experiment, converted into degrees of visual angle toward the target using established methods (Woodman & Luck, 2003). Residual eye movements toward the target averaged less than 0.12 degrees in each observer, which is negligible.
It was not possible to measure eye position during the fMRI experiment. It is extremely unlikely that these well-trained observers made eye movements toward the target, because this would have led to a large change in the position of the target representation in area V1, and no effects of target side were observed in area V1. To further rule out eye movements, we conducted an additional experiment to record eye position from four of the five subjects from the fMRI experiment. In this experiment, subjects performed one run of the fMRI version of the task in the scanner, along with a calibration run. The position of the left eye was measured using a custom-made infrared camera system (modified industrial endoscope). The video data were digitized offline at a rate of 50 frames/s. Eye position data (radial deviation from central fixation in ° of visual angle) were determined within a 500 ms time window beginning with stimulus onset. For the calibration run, the subjects made an eye movement on each trial toward a dot placed at the center of the right or left lower stimulus array. Supplemental Fig. 2b illustrates the amount of eye deviation in the direction of the target. The amount of deviation was small and was consistent with what was obtained in the ERP ERMF experiment. Thus, we can be confident that the results were not significantly distorted by deviations in fixation.
Supplemental References
Woodman, G. F., & Luck, S. J. (2003). Serial deployment of attention during visual search. J Exp Psychol Hum Percept Perform, 29(1), 121-138.
