A Moving Video Window or a Mask Yoked to Eye Movements: Experiments on Letters, Words and Biological Movement with prolonged Hemifield Stimulation

Abstract

We describe the first use of a new technique, which permits prolonged presentation to one or other visual field of complex, realistic, “ecologically valid” stimuli. An infrared eye movement transducer is linked to a visual display such that an electronic mask (of adjustable dimensions) or, alternatively, a “window” can be made to move as a consequence of eye movements. The mask can be made to move exactly with the initiating eye movement, or with positive gain, or in the opposite direction (with or without gain), or in both directions simultaneously (“scissoring”). Alternatively, the apparatus can be set to blank the entire display should an eye movement occur with an excursion greater than a preset criterion level. The display itself can be either computer generated or can consist of a prerecorded video film. We report preliminary findings with this apparatus. When subjects detected a letter target in a three-by-three letter matrix of laterally presented letters, exposure durations from 50 msec to 400 msec showed consistent right visual field (RVF) superiorities. (Nor was there any evidence of left visual-field, LVF, superiorities at very brief exposures as others have claimed.) Equally strong RVF superiorities also appeared when subjects decided whether or not two simultaneously and laterally presented (for 500 msec) words rhymed, the word pairs being phonologically and orthographically similar (DOWN-GOWN), phonologically similar and orthographically distinct (FARE-HAIR), phonologically distinct and orthographically similar (MOWN-DOWN), or both phonologically and orthographically distinct (FORT-GOAT). Finally, Johansson's (1973, 1976) biological movement procedure was adapted for lateral viewing, with unlimited exposure times. However, the predicted LVF superiority did not eventuate, when subjects decided whether moving points of light, attached to the limbs of darkened walkers, were worn by males or females. Further possible applications of this technique are described for normal and clinical subjects.