Leonard S. Mark

Phonetic recoding and reading difficulty in beginning readers.

The results of a recent study (Liberman, Shankweiler, Liberman, Fowler, & Fischer, 1977) suggest that good beginning readers are more affected than poor readers by the phonetic characteristics of visually presented items in a recall task. The good readers made significantly more recall errors on strings of letters with rhyming letter names than on nonrhyming sequences; in contrast, the poor readers made roughly equal numbers of errors on the rhyming and nonrhyming letter strings. The purpose of the present study was to determine whether the interaction between reading ability and phonetic similarity is solely determined by different rehearsal strategies of the two groups. Accordingly, good and poor readers were tested on rhyming and nonrhyming words using a recognition memory paradigm that minimized the opportunity for rehearsal. Performance of the good readers was more affected by phonetic similarity than that of the poor readers, in agreement with the earlier study. The present findings support the hypothesis that good and poor readers do differ in their ability to access a phonetic representation.

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.

The effect of gap depth on the perception of whether a gap is crossable

Four experiments were performed in order to examine the effect of gap depth on human observers’ perception of whether or not a gap is crossable. Experiments 1 and 2 showed that as the gap’s depth increased, observers tended to increasingly underestimate the maximum width of a gap they could step across. Experiments 3 and 4 clarified this finding: The observed covariation of perceived gap crossability and gap depth depended on the observer’s direction of gaze, rather than on the physical depth of the gap. The optical relations to which observers might be attending are discussed, as well as the possibility that cognitive-affective processes might have contributed to observers’ underestimation of their actual capabilities.

Perception of growth: a geometric analysis of how different styles of change are distinguished.

Although there have been many demonstrations that human observers can accurately recognize a variety of styles of change, such as rolling, walking, or growing, there are no existing theories capable of explaining how one style of change is distinguished from another. The present article offers a hypothesis that any recognizable style of change is uniquely specified by geometric invariants- the abstract properties of a visual display that are preserved by the change. In an effort to provide an empirical test of this hypothesis, several experiments involving the perception of growth were performed. Observers were required to make perceptual judgments of consequences of facial profiles, each of which was constructed by using a different mathematical transformation. The same pattern of results was obtained on both a free response task and a growth rating task: All transformations that were consistently identified as growth preserved the same geometric invariants.

Issues related to the prediction of craniofacial growth

The prediction of craniofacial growth involves four central issues: (1) What frame of reference should be adopted for measuring change? (2) What type of coordinate system should be used? (3) How should the change be described? (4) How can the change be explained biologically? In an effort to address these issues within a common framework, we are presenting a mathematical model for predicting the course of craniofacial growth in any given individual. The model is derived from a few basic assumptions about the long-range effects gravitational pressure on the remodeling of bone and is expressed formally as a single geometric transformation. The validity of the model is examined empirically, using data for twenty individuals from the Denver Child Research Councils longitudinal growth study. The predictions of the model are found to be in close correspondence with the actual morphologic changes in each individual over periods ranging from 8 to 17 years. These findings suggest that a transformational approach to the study of human growth may provide clinicians with a valuable tool for long-range treatment planning.

How Do Task Characteristics Affect the Transitions Between Seated and Standing Reaches

In 3 experiments, we examined the effects of task characteristics on the selection of a reach action (mode) when several alternatives are afforded. In the bead pickup task, actors had to skewer a 2-mm bead using a sewing needle. Performing this task entailed significant postural control and visual requirements. The block pickup task involved picking up a 3-cm Lego(r) block using a 2-finger grip, which entailed minimal postural and visual demands. In Experiment 1, as reach distance increased, actors performing the bead task consistently changed to reach modes that afforded greater postural stability at closer distances than they did for the block task. Also, during the bead task actors avoided the partial standing reach mode from which it was difficult to maintain the postural control required to complete the bead task. Mode avoidance was not observed for the block task. Experiment 2 showed that actors changed reach modes at distances at which the relative comfort of 2 reach modes changed. The outcome of Experiment 3 indicated that the selection of action mode, including mode avoidance, was associated more closely with the postural demands of the task than visual requirements. The outcome of this investigation indicates that people choose actions that effect the necessary postural control required to complete the task.

Describing perceptual information about human growth in terms of geometric invariants

Three experiments are reported that examine the perceptual information by which growth of a human head is distinguished from other possible styles of change. The results demonstrate that the perception of growth may be based on a specific set of invariant geometric relations described previously by Mark, Todd, and Shaw (1981). When observers are asked to judge which of two facial profiles looks older, they are surprisingly accurate if the profiles are related by an appropriate transformation, but their performance is no better than chance if the profiles are related by an inappropriate transformation. If, on the other hand, they are instructed to judge whether a pair of profiles is the same or different, the differences produced by the appropriate and inappropriate transformations are equally discriminable.

Facilitate Complex Search Tasks in Hypertext by Externalizing Functional Properties of a Work Domain

The premise of this study was that practical problem solving within a complex work domain (ergonomic design and integration of computer workstations) could be enhanced by a hypertext representation of that work domain. Two alternative hypertext representations were developed. The first consisted of an ecological interface design based on the means-end abstraction hierarchy (AH) approach (Vicente & Rasmussen, 1992). In this design, the goal-relevant constraints and functional relations within the domain were explicitly represented on the interface. The second hypertext interface was based on a more traditional classification hierarchy (CH) in which supraordinate categories were broken down into their components (part-whole relation). The relative effectiveness of the 2 approaches was compared using an experimental procedure in which participants solved ergonomic problems of increasing complexity. The results supported the following research hypotheses: (a) When performing a complex or problem-solving task,...

Visual inertia of rotating 3-D objects

Five experiments were designed to determine whether a rotating, transparent 3-D cloud of dots (simulated sphere) could influence the perceived direction of rotation of a subsequent sphere. Experiment 1 established conditions under which the direction of rotation of a virtual sphere was perceived unambiguously. When a near-far luminance difference and perspective depth cues were present, observers consistently saw the sphere rotate in the intended direction. In Experiment 2, a near-far luminance difference was used to create an unambiguous rotation sequence that was followed by a directionally ambiguous rotation sequence that lacked both the near-far luminance cue and the perspective cue. Observers consistently saw the second sequence as rotating in the same direction as the first, indicating the presence of 3-D visual inertia. Experiment 3 showed that 3-D visual inertia was sufficiently powerful to bias the perceived direction of a rotation sequence made unambiguous by a near-far luminance cue. Experiment 5 showed that 3-D visual inertia could be obtained using an occlusion depth cue to create an unambiguous inertia-inducing sequence. Finally, Experiments 2, 4, and 5 all revealed a fast-decay phase of inertia that lasted for approximately 800 msec, followed by an asymptotic phase that lasted for periods as long as 1,600 msec. The implications of these findings are examined with respect to motion mechanisms of 3-D visual inertia.

Structural support for the perception of growth.

Previous studies have shown that the effects of a particular class of geometric transformations, known as cardioidal strain, are perceived as growth when applied to a variety of animate and even inanimate objects. The current study demonstrates that the effects of these growth transformations are not completely independent of the object undergoing change, but depend critically on certain structural characteristics. When cardioidal strain is applied to a straight-line, right-angle, robotlike structure, there is no consistent effect on the age level of the figure. However, as the structural contours become more curved and less angular, the effects of this transformation are seen as increasingly more like growth. In contrast, the effects of a shear transformation are not perceived as growth on any of the profiles. These findings are examined in light of the critical physical properties that may be responsible for this notion of biological forms as well as their implications for our understanding of the information about events.