Figure 7.

Sensitivity of human V6 to Translational egomotion. (A) Schematic representation of the visual stimulation sequence used in the event-related fMRI experiment. (B) Top: Area V6 mapped with the functional localizer, i.e., coherent flow vs. randomly moving dots (shown in Figure 6A). Results are displayed on a posterior dorso-medial view of the medial folded representation of the left and right hemisphere of the template brain. Bottom: The plots represent the averaged BOLD percent signal change across subjects and hemispheres in the localizer-defined area V6 for each experimental condition labelled as follows: TRA, translational; CIR, circular; RAD, radial; SPI, spiral; RAND, random; STA, static. (C) Sketch of the tridimensional translation stimulus used in the fMRI experiment. [A–C Modified from Sdoia et al. (2009)]. (D) Differential motion parallax. Differential motion parallax is the perceived difference in speed of nearby objects compared to far away ones. Motion parallax is easily perceived when we look through a car window, the velocity of nearby objects appears to be greater than that of distant objects. (E) Optic flow occurs when we are moving in a particular direction. If we look toward the point to which we are heading (the focus of expansion) this doesn't show movement, whereas by looking at the surrounding space, the visual field appears to be expanding. This effect can be perceived with great accuracy by the human brain, contributing to the control of locomotion and helping to continue heading toward the specified location. This effect gives the sense of movement that occurs when we see the famous star field screensaver, which produces the effect of navigating through a field of stars, heading toward a particular point on the screen. [D–E Modified from Ware (1999) “Information Visualization”].