Claudia Carello

Phase transitions and critical fluctuations in the visual coordination of rhythmic movements between people

By watching each others lower oscillating leg, 2 seated Ss kept a common tempo and a particular phase relation of either 0 degrees (symmetric mode) or 180 degrees (alternate mode). This study investigated the differential stability of the 2 phase modes. In Experiment 1, in which Ss were instructed to remain in the initial phase mode, the alternate phase mode was found to be less stable as the frequency of oscillation increased. In addition, analysis of the nonsteady state cycles revealed evidence of a switching to the symmetric phase mode for the initial alternate phase mode trials. In Experiments 2 and 3, Ss were instructed to remain at a noninitial phase angle if it was found to be more comfortable. The transition observed between the 2 phase modes satisfies the criteria of a physical bifurcation--hysteresis, critical fluctuations, and divergence--and is consonant with previous findings on transitions in limb coordination within a person.

Perception of Object Length by Sound

Although hearing is classically considered a temporal sense, everyday listening suggests that subtle spatial properties constitute an important part of what people know about the world through sound. Typically neglected in psychoacoustics research, the ability to perceive the precise sizes of objects on the basis of sound was investigated during the routine event of dropping wooden dowels of different lengths onto a hard surface. In two experiments, the ordinal and metrical success of naive listeners was related to length but not to the simple acoustic variables (duration, amplitude, frequency) likely to be related to it. Additional analysis suggests the potential relevance of an objects inertia tensor in constraining perception of that objects length, analogous to the case that has been made for perceiving length by effortful touch.

Wrinkling and head shape as coordinated sources of age-level information

Changes in the shape of a human head and the development of facial wrinkles were examined as potential sources of information about age level. In Experiment 1, subjects estimated the ages of faces that had been produced by systematically manipulating characteristic head shapes and levels of wrinkles associated with ages 15, 30, 50, and 70 years. The results indicated that observers used both sources of craniofacial change in making age estimates; but the effect of either source of change on perceived age depended upon the level of the other source of change. In Experiment 2, subjects’ ratings of the apparent conflict between levels of head shape and wrinkles further substantiated the conclusion that observers are sensitive to the coordination of products of the two sources of change. These findings suggest that the information specifying perceived age level is a complexrelationship among different types of craniofacial change.

Cognition: The view from ecological realism☆

The term ‘cognition’ is taken, very generally, to refer to the cocxdination of any organism (as an epistemic agent) and its environment (as the support for its acts). The task of cognitive theory is to explain this epistemic, intentional coordination of organism and environment. Orthodoxy subscribes to the Lockean view that the coordination is achieved through, and explained by, a special class of things. Locke called these things that interface organism and environment ‘ideas. ; contemporary cognitive theorists lean toward ‘representaticns’, ‘programs’, ‘reference signals’, ‘schemata’, etc. Each of these coordinating things is an entity presumed to be endowed with properties that are (sometimes loosely, often d-ictlyj isomorphic with those properties of the state of affairs for which the coordinator is said to be causally responsible. Moreover, it is also presumed that a coordinating thing is of the same logical t:?rpe as the organism, snvironment state of affairs that it putatively explainseach ir an instance of intelligence (or knowing, or rationality, or goal-directedness). For the orthodox theorist, an appropriate candidate to play the role of coordiriating thing in a given situation is arrived at by inference: Those properties and that organization that are sufficient to describe .the observed phenomenon must be identified. The assumption is that actual coordinating things are determined similarly, that is, that these instances of i:ntelligence are arrived at intelligently. This view is troublesome on two counts, neither of which seems to bother establishment theorists. First, orthodox cognitive theory is not distressed by the large loans of intelligence that its program demands. Given that coordinating things are rational entities arrived at by rational means, how does orthodox theory account for the ultimate origin of all this rationality? Second, the orthodox view is similarly unconcerned with the skepticism engendered by the assumption that perception is a relation of an organism to an internal representation of its environment. Given that inference can fail, and that the cm-

Affordance, proper function, and the physical basis of perceived heaviness

The physical basis of perceived heaviness requires consideration of the haptic perceptual systems role in controlling actions (the systems proper function) and the relation of an objects inertial properties to properties of the human movement system (the objects affordance). We show that the mass of a wielded object and particular scalar variables calculated from the objects inertia tensor combine linearly in determining perceived heaviness. The tensor-derived scalars reflect the symmetry and volume of the corresponding inertia ellipsoid. These measures bear directly on the objects wieldability, that is, on the patterning and level of muscular forces required to move the object in a controlled fashion.

Effortful touch with minimal movement.

Perception of the extents of occluded rods was examined under conditions in which a rod was held as steadily as possible. A given rod was held horizontally, one one side of its center of mass, with one upward (U) and one downward (D) force. Extent was perceived when D and U were distributed over the surfaces of 1 hand, 2 hands, and a hand and a knee and if only D or only U was provided anatomically, the other being provided by an environmental support. Increasing the distance between D and U decreased perceived extent when both contact points were anatomical and when only 1 was anatomical. The first moment of the mass distribution, a constant, affcted perceived extent more than gravitational torque, a variable. Rods of different lengths but of the same first moment were not distinguished

Physics and Psychology of the Muscle Sense

The sensibility associated with muscles contributes little to the conceptual content of current psychology. In part, this is because perceptions achieved through the muscle sense typically go unnoticed. Nonetheless, researchers have discovered a rich variety of muscle-based perceptual capabilities—such as those relating to held objects, probed objects, and body segments—that seem to depend on quantities well known in physics, quantities that reflect how the mass of an object or limb is distributed. The conceptual and technical issues posed by these capabilities warrant study by psychologists interested in the general problems of space perception, action, and selective attention.

Haptically Creating Affordances: The User-Tool Interface

Successful use of a hand-held tool requires overcoming the rotational inertia of the hand-plus-tool system. Where an object is grasped affects this rotational inertia. Appropriate choice of grip position may be crucial in the safe, effective, and efficient control of a hand-held tool. In 3 experiments, the authors investigated how choice of grip position on a tool was constrained by task demands. The results suggest that choice of grasp position serves to establish relationships among 3 variables derived from the inertial ellipsoid of the hand-object system (volume, symmetry, and eigenvector angle) in a way that specifically reflected the power or precision constraints of the given task. These variables have previously been shown to play a role in haptic perception of tool function. Changing grasp position on a tool is a way to exert control over the nuances of the user-tool interface.

Perceiving the sweet spot.

Many sports involve aligning a hitting implement with a ball trajectory such that contact is made at the implements center of percussion or ‘sweet spot’. This spot is not visibly distinct; its perception must be haptic. Although it is functionally defined with respect to contact—it is the point of impact that produces the least vibration in the hand holding the implement—hitting success requires appreciating the location of the sweet spot prior to contact. Two experiments verified that perceivers (novices as well as expert tennis players) distinguished perception of length from perception of the position of the sweet spot simply on the basis of wielding, both for tennis rackets and for bats contrived from wooden rods with attached masses. Results conformed to previous research on dynamic touch in showing that perceiving the lengths of wielded objects, including selectively perceiving partial lengths, is constrained by inertial properties of the object.

Metamers in the haptic perception of heaviness and moveableness

It is hypothesized that heaviness perception for a freely wielded nonvisible object can be mapped to a point in a three-dimensional heaviness space. The three dimensions are mass, the volume of the inertia ellipsoid, and the symmetry of the inertia ellipsoid. Within this space, particular combinations yield heaviness metamers (objects of different mass that feel equally heavy), whereas other combinations yield analogues to the size-weight illusion (objects of the same mass that feel unequally heavy). Evidence for the two types of combinations was provided by experiments in which participants wielded occluded hand-held objects and estimated the heaviness of the objects relative to a standard. Further experiments with similar procedures showed that metamers of heaviness were metamers of moveableness but not metamers of length. A promising conjecture is that the haptic perceptual system maps the combination of an object’s inertia for translation and inertia for rotation to a perception of the object’s maneuverability.