Hugo Bruggeman

The Direction of Walking—but Not Throwing or Kicking—Is Adapted by Optic Flow

Optic flow is known to adapt the direction of walking, but the locus of adaptation remains unknown. The effect could be due to realignment of anatomical eye, head, trunk, and leg coordinate frames or to recalibration of a functional mapping from the visual direction of the target to the direction of locomotion. We tested whether adaptation of walking to a target, with optic flow displaced by 10°, transfers to facing, throwing, and kicking a ball to the target. A negative aftereffect for initial walking direction failed to transfer to head orientation or throwing or kicking direction. Thus, participants effectively threw or kicked the ball to the target, and then walked in another direction to retrieve it. These findings are consistent with recalibration of a task-specific visuo-locomotor mapping, revealing a functional level of organization in perception and action.

Biomechanical versus Inertial Information: Stable Individual Differences in Perception of Self-Rotation.

When turning without vision or audition, people tend to perceive their locomotion as a change in heading relative to objects in the remembered surroundings. Such perception of self-rotation depends on sensitivity to information for movement from biomechanical activity of the locomotor system or from inertial activation of the vestibular and postural systems. The authors report 3 experiments that investigated the relative contributions of biomechanical and inertial information to perceiving the speed of self-rotation. Using a circular treadmill, the proportions of the 2 sources of proprioceptive information were varied, creating walking conditions with a constant rate of biomechanical activity but with variable speeds of rotation relative to inertial space. The results reveal stable individual differences in sensitivity to information for the perception of locomotion. Just more than half of the participants based their perceived speed of self-rotation on biomechanical information, whereas the others based theirs on inertial information.

Learning to throw on a rotating carousel: recalibration based on limb dynamics and projectile kinematics.

Abstract Skilled actions exhibit adjustment in calibration to bring about their goals. The sought-after calibrations change as a function of the environmental situation that stages the actions. In these experiments participants sat on one side of a rotating carousel and threw beanbags underhanded at a target fixed on the opposite side. Logically, aimed throwing in this situation involves adjustment to fit changes in limb dynamics (originating from Coriolis forces) and changes in perceived projectile kinematics (originating from the tangential velocity of thrower and target). We studied whether such adjustment involved one or multiple components of recalibration. An initial experiment showed that exposure to rotation while throwing beanbags produced a robust recalibration in the direction of underhanded throws as manifest in throwing at stationary targets from a stationary position. Following some initial decay this recalibration persisted and approached an asymptote. Subsequent experiments suggested two independent components of recalibration. One is based on limb dynamics and accounts for the initial decay. The other is based on the perceived projectile kinematics and accounts for the stable change in throwing direction. These results raised the question of how multiple components of recalibration of an action are related. We propose that movement components are independent and calibrated separately at different levels in the organization of an action.

Psychophysics of reading. XIX. Hypertext search and retrieval with low vision

For pt. XVIII see Vis. Res., vol. 38, no. 19, pp. 2949-62 (1998).Low vision is any chronic form of visual impairment, not correctable by glasses or contacts that adversely affects performance of important everyday visual tasks. Most people with low vision need magnified text to read. On a fixed-size computer screen, the magnification of text trades off against the proportion of the entire screen visible. To read hypertext, simultaneous access to the full-screen page is important for skimming text and for locating hyperlinks. Therefore, people with low vision using magnified text might encounter difficulties reading hypertext, especially when hyperlinks are placed at unpredictable locations (true for most webpages). We investigated hypertext information retrieval as the time taken and number of nodes traversed to answer a series of questions. In Experiment 1, low-vision performance for reading prose and hypertext was compared to normal performance: low-vision performance deficits in hypertext retrieval were predictable from deficits in conventional prose reading. Experiment 2 evaluated the effect of web-page layout on low-vision performance: retrieval performance was severely affected when hyperlinks had unpredictable locations. This extra deficit was eliminated when users were provided with simultaneous access to full-screen layout. Based on these findings, we discuss the accessibility of the Internet by people with low vision.

Dynamic Manipulation Generates Touch Information That Can Modify Vision

>> This report constitutes a critical expansion of a recent study on tool use (Carlson, Alvarez, Wu, & Verstraten, 2010), published in this journal. Carlson et al. explored the classic question of how, during manipulation, an external object may seem to become an extension of one’s body. They demonstrated that objects manipulated with the hand can become one with the body, but objects manipulated with a tool cannot. They interpreted this as evidence that such integration is limited to first-order extensions. However, close inspection of the experimental conditions reveals that Carlson et al. overlooked how dynamic manipulation of an object affects the prehensile system. They used just one tool: a pair of grippers fixed to, and supported by, a table. In this arrangement, the table absorbs most of the forces associated with object manipulation. By contrast, when a freely maneuverable handheld tool is used, the forces are transmitted through the tool and interact with the arm and body, much as they do during direct manual manipulation. The notion that, without vision, object properties such as the length of a handheld rod can be perceived during dynamic manipulation has been well established. This system of touch perception is known as dynamic touch— perception based on information from effort-related muscle and tendon deformations (Carello & Turvey, 2000; Gibson, 1966; Turvey, 1996; Turvey & Carello, 2011). However, little is known about the perception of a target object when it is manipulated with a handheld tool. We concluded that the approach used by Carlson et al. would be a useful way to test such perception empirically, and we extended their conditions to include one with a freely maneuverable tool. Moreover, we predicted that the target object would be perceived with and without a tool, but only when the prehensile limb was maneuvering freely.

The role of Binocular Information in the Control of Perception and Action

We investigated perceptual judgements and pointing movements towards edges of a trapezoid window. The trapezoid window depicts geometrical information suggesting a slanted display. Viewed monocularly, it provides a powerful depth illusion, whereas the window is perceived as a flat object when viewed binocularly.