A causal role for the right frontal eye fields in value comparison
- Departments of Psychology, Economics, The Ohio State University, United States
- Zurich Center for Neuroeconomics, Department of Economics, University of Zurich, Switzerland
- Decision Neuroscience Lab, Depterment of Heatlh Sciences and Technology, ETH Zurich, Switzerland
Figures
Figure 1
Experiment setup. (A) Rating-task timeline: Subjects saw each food item for 2 s and then rated how much they would like to eat it on a scale from 0 to 10, or excluded the item by pressing the space bar (no time limit).
(B) Choice-task timeline: Subjects first had to fixate a central cross for 2 s. They then had to choose between the two presented food items using the keyboard. The chosen food was then highlighted for 1 s. (C) Histogram of overall value (OV) in the choice task: Trials were constructed to have either very high or low OV. (D) Stimulation: After the rating task, subjects received continuous theta-burst transcranial magnetic stimulation (TMS) over the vertex (left panel) or right frontal eye field (FEF) (right panel), depicted here schematically by the small green TMS coil symbol over one subject’s brain reconstruction.
Figure 2
Simulations of the attentional drift diffusion model (aDDM).
To provide an intuition for why the aDDM makes different predictions for low and high overall value (OV), we simulated the aDDM, once with low values (dashed lines) and once with high values (solid lines). The simulations were run for a subject with a typical gaze discount factor (low θ-value, blue line) (θ = 0.3) and a subject with less of a discount (red line) (θ = 0.5). Dark (light) gray areas indicate periods where the subject is looking at the left (right) item. The relative decision value (V) evolves over time with a slope that is biased toward the item that is being fixated. The left item is selected when V reaches an upper boundary and the right item is selected when V reaches a lower boundary. (A) For a given θ, higher OV results in bigger changes in the slope (drift rate) when gaze shifts between left and right. (B) For low OV, shifts in gaze lead to little change in drift rate regardless of θ. (C) For high OV, shifts in gaze lead to large changes in drift rate, particularly for lower θ. Taken together, this means that the behavioral difference between low and high θ is much more pronounced for high vs. low OV. In particular, larger changes in drift rate lead to faster decisions and a stronger propensity to choose the longest fixated option.
Figure 3
Frontal eye field (FEF) effects on gaze patterns.
Probability of looking first at the left food item during a trial. Subjects had a strong tendency to look left first. This tendency was slightly reduced in high vs. low overall value (OV) trials for the vertex group but not the FEF group. Bars are s.e.m., and the x-coordinates of the points are jittered around the true values of –1, 0, and 1.
Figure 4
Behavioral results.
The left panels are for low overall value (OV) trials, the right panels are for high OV trials, and vertex subjects are displayed in blue, frontal eye field (FEF) subjects in red. (A) Choice data: The probability of choosing the left item as a function of the total dwell time difference between the left and right items. Quintiles were determined at the subject level. Quintile 0 represents decisions where both items had similar total dwell times. Negative quintiles indicate more dwell time for the right item and positive quintiles indicate more dwell time for the left item. Bars are s.e.m. (B) Density plots of log reaction time (RT) for low and high OV, respectively.
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A causal role for the right frontal eye fields in value comparison
eLife 10:e67477.
https://doi.org/10.7554/eLife.67477
