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Biomedical subjects

C von Hofsten

Publications and source records attributed to C von Hofsten.

14 recordsLinked to original sources
PubMed1992

Gravity as a monocular cue for perception of absolute distance and/or absolute size.

When the motion of an object is influenced by gravity (eg free fall, pendulum, wave motion), that influence may provide a cue to computing the absolute distance and/or size of the object. Formal analysis supports the claim that the distance and size of moving objects are generally computable with reference to the gravitational component of motion. Informal evidence from judgments of realism in films is consistent with this gravity-cue hypothesis.

Cues↗
PubMed1991

Infants' sensitivity to differential luminance as information about depth.

To what degree are young infants able to perceive differential shadowing and to what degree are they able to utilize this stimulus parameter as information about depth? Two habituation experiments were performed. In Experiment 1, a group of 5-month-old infants were habituated to a low frequency, vertical, and approximately sinusoidal luminance grating superimposed on a flat colored surface. This display induced stable 3-D perception in adult subjects. After habituation, the infants viewed two test displays at alternating trials. One was made up of real half cylinders matching the light distribution of the habituation display and the other was made up of a square wave grating of the same spatial frequency as in the habituation one. Adults perceived the latter display as flat. Results showed that both test displays were treated as new ones by the infants habituated to the sinusoidal grating. Experiment 2 was identical to Experiment 1, except that the subjects were 3 1/2-month-old. These infants treated the half cylinders as familiar and the square wave grating as new. The results indicate that infants at both age levels (3 1/2 and 5 months of age) were sensitive to the difference between sharp and gradual change in luminance which is a prerequisite for perceiving form from luminance. However, neither age group seemed to utilize gradual change in luminance as information about space.

Attention↗
PubMed1988

The integration of sensory information in the development of precise manual pointing.

The development of manual pointing was studied in 270 children from 4 yr of age to 12 yr of age. Fifteen boys and 15 girls were included in each age group. The task was to place pins underneath a table-top at positions seen or felt on the table-top. Each child was tested in four different conditions: both visual and proprioceptive information about the position of the dot to be pointed at could be provided, just one of these two sources of information could be provided, or none of them. Errors were analysed in terms of systematic and random error. The results show that in all age groups, performance was superior when visual information about the position of the dot was provided. The ability to utilize visual information was found to be rather good already at the youngest ages. In the visual conditions the random error decreased with age in a gradual and linear fashion but the systematic error did not, it decreased and increased and decreased again. Errors were substantially smaller at 7 and 11 yr of age. The ability to use information from the proprioceptors improved remarkably during the youngest ages. All the improvement of the random error between 4 and 5 yr of age could be attributed to this factor. The systematic error in all conditions was found to be displaced towards the contralateral side of the body, but this effect was strongest in the proprioceptive condition. A strong interaction between sex and hand used in pointing was found in the systematic errors but none in the random errors. The interaction could be described as a nondominant hand disadvantage of the girls.

Attention↗
PubMed1988

Preparation for grasping an object: a developmental study.

The development of visually controlled grasping actions was studied in two experiments. An optoelectronic technique (SELSPOT) was used to monitor the opening and closing of the hand during reaching actions by measuring the change in the distance between thumb and index finger. The purpose of Experiment 1 was to establish an adult criterion for the development. It was shown that adults started closing the hand around the target well before touch and that the timing was dependent on the size of the target. The hand started to close earlier when grasping a small rather than a large target. In addition, the degree of hand opening was also less for a small than for a large target. In Experiment 2 it was shown that infants who were 5-6, 9, and 13 months of age also controlled their grasping actions visually and started closing the hand around the target in anticipation of the encounter rather than as a reaction to the encounter. However, the strategy of the two younger age groups was different from that of adults. They started closing the hand closer to the time of contact with the target than did the 13-month-olds, who were comparable to adults in this respect. The timing was not dependent on the size of the target in any of the infant groups. In all age groups, reaching and grasping were most commonly organized in a continuous way; that is, the hand started to close without any interruption in the approach. The opening of the hand was found to be adjusted to target size in the 9- and 13-month-olds but not in the 5-6 month olds.

Adult↗
PubMed1986

Do infants reach for perceived objects? A reply to Stiles-Davis.

Stiles-Davis proposes that the infants in our experiments (Hofsten & Spelke, 1985) did not reach for perceived objects in order to manipulate them, but rather touched perceived surfaces in order to explore their boundaries. Her commentary raises questions about infants' perception of the boundaries, the unity, and the manipulability of objects. More deeply, it raises the question of what an object is for an infant. We consider each of these questions in turn, in light of our own findings and those of other studies of object-directed reaching, object perception, and the object concept. We suggest that young infants organize the visual world into entities that are bounded, unitary, and manipulable and that infants endow those entities with the core properties of physical objects.

Concept Formation↗
PubMed1985

Object perception and object-directed reaching in infancy.

Five-month-old infants were presented with a small object, a larger object, and a background surface arranged in depth so that all were within reaching distance. Patterns of reaching for this display were observed, while spatial and kinetic properties of the display were varied. When the infants reached for the display, they did not reach primarily for the surfaces that were nearer, smaller, or presented in motion. The infants reached, instead, for groups of surfaces that formed a unit that was spatially connected and/or that moved as a whole relative to its surroundings. Infants reached for the nearer of two objects as a distinct unit when the objects were separated in depth or when one object moved relative to the other. They reached for the two objects as a single unit when the objects were adjacent or when they moved together. The reaching patterns provided evidence that the infants organized each display into the kind of units that adults call objects: manipulable units with internal coherence and external boundaries. Infants, like adults, perceived objects by detecting both the spatial arrangements and the relative movements of surfaces in the three-dimensional layout.

Depth Perception↗
PubMed1979

Recalibration of the convergence system.

Adaptation to convergence-altering prism spectacles was studied. The subjects were trained for 8 min with either convergence-increasing or convergence-decreasing prisms. Before and after training they estimated the distance to a binocular dot varying in the stimulus it provided to convergence. Both the preadaptation and postadaptation estimates showed that the reciprocal of estimated target distance is linearly related to convergence. Further there was a consistent change in the direction of adaptation expected from the preadaptation to the postadaptation test. This change was accounted for in terms of a recalibration of the effective absolute convergence level.

Adaptation, Ocular↗
PubMed1977

Binocular convergence as a determinant of reaching behavior in infancy.

Reaching behavior in eighteen- to thirty-two-week-old infants was studied as a function of binocular convergence. The infant looked at the object to be reached for through prism arrangements which changed convergence only. The reaches obtained were nearly always directed at the virtual object defined by convergence. Corrections of the reaches, if any, were made rather late and often not before the hand arrived at the place of the virtual object.

Age Factors↗