The “X’(extreme) periphery” can be defined by visual eccentricity larger than 60 deg., up to the limit of the visual field (90 deg., approximately). This should be of the central focus of vision scientists who are interested in the situations where the brain needs to solve the maximum degree of ambiguity in visual inputs. Ironically, very little has been studied and known. Thus, we have conducted a series of experimental studies to test our “brain compensation hypothesis” in the past one decade or so, which are reviewed in this talk with three main themes.
1) Auditory-visual integration. A flicker appears faster in the periphery than that with the same frequency (say 5Hz) in the fovea, but they can be entrained by synchronous sounds. An auditory primer not always facilitate visual detection, but it does so when motion direction is consistent (visual moving motion with auditory Doppler stimulus), or at a particular frequency (eg. 300 Hz).
2) Color/location cluttering. Colors and locations are often misperceived in the X’periphery, especially when crowded. Not only that there are color/relative location mistakes, some new phenomenological effects are reported in the X’periphery, such as flashing, dynamic changes of color, filling-in, etc. A cortical-magnification-like factor tends to be found when the critical size for such illusions is measured at each eccentricity.
3) Action capture. When the observer moves its own hand behind the display, which can be either dynamic random noise or a low-frequency (say 2-3 Hz) flicker, the visual stimulus is often “captured” by the hand, thus appear to move along with it. Own action tends to yield somewhat stronger effect than observing other’s, but the latter still yields a substantial capture effect.

In short, the effects that have been found in the periphery are enhanced or qualitatively extended (ie. new effects are found) in the X’periphery. A large part of the findings can be accounted for by the cortical magnification, in that the same size-dependent perceptual processing operates across eccentricities (including the X’periphery) and that it is just the size scaling differences. Related to this, we still need to make two points. First, even if it is just cortical magnification, the psychophysical findings in the X’periphery would have a wide and profound impacts in the real-world situations, including driving, VR and display technology, sports, entertainment, etc. Second and more significantly, there is something more noticeable, on top of what would be expected from the cortical magnification - especially related to clarity/stability and confidence on the percept in the X’periphery. At a glance, it may be puzzling as to why invalid (illusory) percept with confidence is adaptive or beneficial in any fashion. From the biological and evolutionary perspective, a quick “false alarm” can often be better than a slow “hit” or no decision, especially when it comes to risk detection.

To conclude, the mystery of the X’periphery is multi-layered, some of which are yet unsolved.

(This talk will be given orally in Japanese, with the slides mostly in English.)

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