Alen Hajnal

Palm boards are not action measures: An alternative to the two-systems theory of geographical slant perception

Whereas most reports of the perception of outdoor hills demonstrate dramatic overestimation, estimates made by adjusting a palm board are much closer to the true hill orientation. We test the dominant hypothesis that palm board accuracy is related to the need for motor action to be accurately guided and conclude instead that the perceptual experience of palm-board orientation is biased and variable due to poorly calibrated proprioception of wrist flexion. Experiments 1 and 3 show that wrist-flexion palm boards grossly underestimate the orientations of near, reachable surfaces whereas gesturing with a free hand is fairly accurate. Experiment 2 shows that palm board estimates are much lower than free hand estimates for an outdoor hill as well. Experiments 4 shows that wrist flexion is biased and noisy compared to elbow flexion, while Experiment 5 shows that small changes in palm board height produce large changes in palm board estimates. Together, these studies suggest that palm boards are biased and insensitive measures. The existing literature arguing that there are two systems in the perception of geographical slant is re-evaluated, and a new theoretical framework is proposed in which a single exaggerated representation of ground-surface orientation guides both action and perception.

Slant perception in near space is categorically biased: Evidence for a vertical tendency

The geographical slants of hills are known to appear quite exaggerated. Here, we examine the visual and haptic perception of the geographical slant of surfaces within reach under full-cue conditions and show that the perceived orientation of even these surfaces is biased. An exaggeration with respect to deviations from horizontal is shown to be present cross-modally. Experiment 1 employed numerical estimation to show the effect for visually observed surfaces, while controlling for verbal numerical bias. Experiment 2 demonstrated that the bias is present even when manual measures show good calibration. Experiment 3 controlled for direction of gaze. Experiment 4 measured the same bias for haptic surfaces. Experiment 5 showed that the bias can also be observed using the nonnumeric task of angle bisection. These results constrain theories of geographical slant perception and appear most consistent with functional scale expansion of deviations from horizontal.

The Perceptual Experience of Slope by Foot and by Finger

Historically, the bodily senses have often been regarded as impeccable sources of spatial information and as being the teacher of vision. Here, the authors report that the haptic perception of slope by means of the foot is greatly exaggerated. The exaggeration is present in verbal as well as proprioceptive judgments. It is shown that this misperception of pedal slope is not caused by calibration to the well-established visual misperception of slope because it is present in congenitally blind individuals as well. The pedal misperception of slope is contrasted with the perception of slope by dynamic touch with a finger in a force-feedback device. Although slopes feel slightly exaggerated even when explored by finger, they tend to show much less exaggeration than when equivalent slopes are stood on. The results are discussed in terms of a theory of coding efficiency.

Transfer of calibration between hand and foot: Functional equivalence and fractal fluctuations

Transfer of competency in a perceptual task often depends on shared information between anatomically different perceptual subsystems. The problem of studying transfer involves isolating conditions of similarity and then trying to account for any resulting differences in transfer. To respect this twofold aspect, this article takes a two-pronged approach to transfer in dynamic touch. The present research first tests the hypothesis that functional equivalence supports the transfer of dynamic touch. Participants were trained to wield unseen objects with the hand or foot and were then tested on anatomically disparate limbs (i.e., the foot or hand, respectively). Next, we examined motion capture of these wielding behaviors for predictors of any asymmetry in transfer. Temporally fractal fluctuations of exploratory behavior can modulate information detection, and we tested whether the fractality of wielding might predict asymmetries in transfer across disparate limbs. Results suggest that transfer of training to anatomically disparate limbs respects functional conditions of similarity and also that the degree of temporally fractal fluctuations predicted limb differences in transfer.

Haptic selective attention by foot and by hand

Nonvisual perceptions of a wielded objects spatial properties are based on the quantities expressing the objects mass distribution, quantities that are invariant during the wielding. The mechanoreceptors underlying the kind of haptic perception involved in wielding - referred to as effortful, kinesthetic, or dynamic touch - are those embedded in the muscles, tendons, and ligaments. The present experiments focus was the selectivity of this muscle-based form of haptic perception. For an occluded rod grasped by the hand at some intermediate position along its length, participants can attend to and report selectively the rods full length, its partial lengths (fore or aft of the hand), and the position of the grip. The present experiment evaluated whether participants could similarly attend selectively when wielding by foot. For a given rod attached to and wielded by foot or attached to (i.e. grasped) and wielded by hand, participants reported (by magnitude production) the rods whole length or fractional length leftward of the point of attachment. On measures of mean perceived length, accuracy, and reliability, the degree of differentiation of partial from full extent achieved by means of the foot matched that achieved by means of the hand. Despite their neural, anatomical, and experiential differences, the lower and upper limbs seem to abide by the same principles of selective muscle-based perception and seem to express this perceptual function with equal facility.

Lateral ball interception: hand movements during linear ball trajectories

Part of understanding how acts are coordinated is identifying the information that guides movements. In the case of catching a ball within arm’s reach, that identification has been complicated by empirical disparities concerning hand-movement reversals during catching. Jacobs and Michaels (J Exp Psychol Hum 32: 443–458, 2006) found unilateral reversals in a paradigm in which balls swung down in an arc; this implicated a particular optical variable, the ratio of lateral velocity to expansion velocity. Montagne et al. (Exp Brain Res 129:87–92, 1999) reported bilateral reversals when balls approached along a linear trajectory, which implicated a different variable, lateral ball position. The research reported here attempted to replicate Montagne et al.’s (Exp Brain Res 129:87–92, 1999) findings. In Experiment 1, participants caught balls rolling toward them across a table, under full lighting using monocular or binocular viewing; in Experiment 2, participants caught luminous balls with a luminous glove in an otherwise dark room. Using Montagne et al.’s (Exp Brain Res 129:87–92, 1999) criterion, we observed no movement reversals in any condition, though some aspects of hand movements suggested the relevance of lateral ball position. The results of Experiment 3, which asked perceivers to indicate only where rods pointed, suggested that lateral position effects were a bias that is unrelated to interception. The ratio of lateral velocity to expansion appears to be a better variable for explaining hand trajectories in lateral interception.

Task specificity and anatomical independence in perception of properties by means of a wielded object.

Behavior is typically organized with respect to a goal to be achieved rather than the anatomical components used in doing so. Similarly, perception is typically organized with respect to a property to be perceived rather than the anatomical components used in doing so. Such task specificity and anatomical independence is manifest in perception of properties of a wielded object. In 6 experiments, we investigated whether these properties might also be manifest in perception of properties by means of a wielded object. In particular, we investigated perception of whether a surface could be stood on when the object used to explore that surface is wielded by the preferred and nonpreferred hands (Experiment 1), by 1 or both hands (Experiment 2), by different 2-handed grips (Experiment 3), and by entirely different limbs (i.e., the hand and the foot, Experiments 4-6). In general, the results show that perception reflected the action capabilities of the perceiver but was largely unaffected by the (configurations of) anatomical components used to wield the object. The results highlight the haptic system as a smart perceptual device and as a multifractal biotensegrity structure.

Location but not amount of stimulus occlusion influences the stability of visuo-motor coordination.

The current study examined whether the amount and location of available movement information influenced the stability of visuo-motor coordination. Participants coordinated a hand-held pendulum with an oscillating visual stimulus in an inphase and antiphase manner. The effects of occluding different amounts of phase at different phase locations were examined. Occluding the 0°/180° phase locations (end-points) significantly increased the variability of the visuo-motor coordination. The amount of occlusion had little or no affect on the stability of the coordination. We concluded that the end-points of a visual rhythm are privileged and provide access to movement information that ensures stable coordination. The results are discussed with respect to the proposal of Bingham and colleagues (e.g., Bingham GP. Ecol Psychol 16:45–53, 2004a; Wilson AD, Collins DR, Bingham GP. Exp Brain Res 165:351–361, 2005a) that the relevant information for rhythmic visual coordination is relative direction information.

Use your head! Perception of action possibilities by means of an object attached to the head.

Abstract Perceiving any environmental property requires spontaneously assembling a smart perceptual instrument—a task-specific measurement device assembled across potentially independent anatomical units. Previous research has shown that to a large degree, perception of a given environmental property is anatomically independent. We attempted to provide stronger evidence for this proposal by investigating perception by an organization of anatomical and inert components that likely requires the spontaneous assembly of a novel smart perceptual instrument—a rod attached to the head. Specifically, we compared cephalic and manual perception of whether an inclined surface affords standing on. In both conditions, perception reflected the action capabilities of the perceiver and not the appendage used to wield the rod. Such results provide stronger evidence for anatomical independence of perception within a given perceptual system and highlight that flexible task-specific detection units can be assembled across units that span the body and inert objects.

Perceiving Action-Relevant Properties of Tools Through Dynamic Touch: Effects of Mass Distribution, Exploration Style, and Intention

At issue in the present series of experiments was the ability to prospectively perceive the action-relevant properties of hand-held tools by means of dynamic touch. In Experiment 1, participants judged object move-ability. In Experiment 2, participants judged how difficult an object would be to hold if held horizontally, and in Experiments 3 and 4, participants rated how fast objects could be rotated. In each experiment, the first and second moments of mass distribution of the objects were systematically varied. Manipulations of wielding speed and orientation during restricted exploration revealed perception to be constrained by (a) the moments of mass distribution of the hand-tool system, (b) the qualities of exploratory wielding movements, and (c) the intention to perceive each specific property. The results are considered in the context of the ecological theory of dynamic touch. Implications for accounts of the informational basis of dynamic touch and for the development of a theory of haptically perceiving the affordance properties of tools are discussed.