Nonvisual navigation by blind and sighted: assessment of path integration ability.

Blindfolded sighted, adventitiously blind, and congenitally blind subjects performed a set of navigation tasks. The more complex tasks involved spatial inference and included retracing a multisegment route in reverse, returning directly to an origin after being led over linear segments, and pointing to targets after locomotion. As a group, subjects responded systematically to route manipulations in the complex tasks, but performance was poor. Patterns of error and response latency are informative about the internal representation used; in particular, they do not support the hypothesis that only a representation of the origin of locomotion is maintained. The slight performance differences between groups varying in visual experience were neither large nor consistent across tasks. Results provide little indication that spatial competence strongly depends on prior visual experience.

Rubbing your stomach while tapping your fingers: interference between motor planning and semantic judgments.

Previous research (Klatzky et al., 1989) shows that the time required to make sensible/nonsensible judgments about an action-object phrase (e.g., "rub your stomach") is reliably faster when the phrase is preceded by a cure representing a specific prototypical hand shape (vs. a neutral cue). The current experiments investigated the effects of preparing for an alternate task (finger tapping vs. syllable vocalization) on facilitatory priming of sensibility judgments. Preparation for finger tapping reduced the magnitude of the priming effect more than preparation for vocalization, suggesting that resources accessed during semantic processing of action-object phrases are also used during manual response preparation. The results support the existence of a system representing manual actions that is limited in the number of activities that can be represented at one time and that is not so general that it represents manual and vocal tract movements.

Stimulus complexity effects in visual comparisons: the effects of practice and learning context.

This study examined visual comparison performance for 6-24-point random polygon stimuli (Cooper & Podgorny, 1976). Stimulus complexity effects decreased with practice, consistent with Bethell-Fox and Shepard (1988). A difficult discrimination context produced greater complexity effects than an easy discrimination context, consistent with Folk and Luce (1987). The difficult discrimination context also led to more stimulus-specific learning and diminished stimulus complexity effects. Increased stimulus learning resulted in continued skill acquisition, better transfer, and less performance disruption when the task context was equated for all Ss. It is argued that improvements in performance in a perceptual comparison task are not solely a function of the amount of practice provided in responding to particular stimuli. The context in which responses are elicited is equally important and must be accommodated in theories of skill acquisition.

Perceptual and cognitive factors governing performance in comparative arrival-time judgments.

Four experiments were conducted to investigate factors affecting relative arrival-time judgments in the transverse plane. Across experiments, results indicated an overreliance on relative distance information. The levels of relative velocity and distance used in the arrival-time task were proved discriminable, and performance in both relative velocity and distance judgments predicted performance in the relative arrival-time task. Despite the distance bias, an attempt to integrate relative velocity and distance information was also evidenced. The distance bias appears to have resulted from resource limitations on the concurrent processing of relative velocity and distance information, causing relative velocity information to become resource limited. The final experiment assessed the stability of performance in each of the tasks over time and provided evidence of individual differences in the ability to coordinate information from multiple sources.

Planning for hand shape and arm transport when reaching for objects.

Two early components of object manipulation are shaping the hand appropriately for functional interaction and transporting the arm with appropriate force and spatial precision to the target object. Three experiments addressed whether people plan these two components before the onset of reaching and if so, how the plans are coordinated. Subjects reached for and contacted a series of objects with one of four hand configurations: pinch, poke, palm, and clench. The required configuration was signaled by the object's color; in some conditions its structure provided a redundant cue. The time from object exposure to arm liftoff (reaction time: RT) and the time from liftoff to contact (movement time: MT) were recorded. In Experiment 1, a compatible stimulus-to-hand-shape mapping substantially facilitated RT but not MT, suggesting that the appropriate hand shape was planned prior to reaching. Experiment 2 showed that contact precision, as defined by the stability of the object's support plane, affected MT; a smaller RT effect also suggested some pre-movement planning of arm transport to accommodate precision demands. Experiment 3 combined compatibility and precision manipulations in a single task to test a model which proposes that planning for hand-shape and arm transport occur in parallel, with the onset of reaching deferred until the slower planning process is completed.

Timecourse of preshaping for functional responses to objects.

The present study explores the unfolding of hand shaping the context of functional responding to common objects. The principal issue addressed by this study is whether distinct, identifiable preshapes are evidenced in preparation for four distinct types of hand contact, including nonprehensile as well as prehensile hand shapes, and for small and large surfaces of contact. All four shapes considered here (poke, pinch, palm and clench) showed evidence of distinct preshaping, with similar timecourses in relation to the onset of reaching. The initial separation of the fingers, formation of first identifiable preshape feature, and completion of the preshape appeared at essentially the same time relative tot he onset of reaching for all four hand shapes. The hand shapes did differ, however, in the time between the completion of a stable preshape and contact with the object. The time for preshape-to-contact was greater for hand shapes with small surfaces of contact than for those with large surfaces and for prehensile shapes than for nonprehensile. These differences are attributed to the precision required for the ultimate object-contact response.

Acquisition of route and survey knowledge in the absence of vision.

The ability of sighted, blindfolded individuals to navigate while walking was assessed in two types of tasks, one requiring knowledge of a route that previously had been navigated and another requiring more complex spatial inference or computation. A computerized measurement system monitored spatial position. The route tasks included maintenance of a heading, distance and turn reproduction and estimation, and turn production. The inferential task required completion of a multisegment pathway by returning directly to the origin. pathways were replicated at two different scales. Measures for the route-knowledge tasks indicated a substantial ability to navigate in the absence of visual cues. Route reproduction performance was particularly accurate despite intrinsic veering tendencies. A substantial increase in error was observed in the pattern-completion task. Errors in pathway completion increased with pathway complexity and were quite similar in the two scales. Correlational data suggested that performance on different route-knowledge tasks reflected differing underlying representations. The completion task led to a high correlation between absolute turn and distance error but had minimal correlations with the route tasks. The data suggest that a survey representation with some degree of scale independence was constructed for use in the pathway completion task.

Acoustic and semantic interference effects in words and pictures.

Interference effects for pictures and words were investigated using a probe-recall task. Word stimuli showed acoustic interference effects for items at the end of the list and semantic interference effects for items at the beginning of the list, similar to results of Kintsch and Buschke (1969). Picture stimuli showed large semantic interference effects at all list positions with smaller acoustic interference effects. The results were related to latency data on picture-word processing and interpreted in terms of the differential order, probability, and/or speed of access to acoustic and semantic levels of processing. A levels of processing explanation of picture-word retention differences was related to dual coding theory. Both theoretical positions converge on an explanation of picture-word retention differences as a function of the relative capacity for semantic or associative processing.

Hemisphere differences for components of mental rotation.

The hemispheric functional lateralization of components of mental rotation performance was investigated. Twenty right-handed males were presented with rotated alphanumerics and unfamiliar characters in the left or right visual field. Subjects decided if the laterally presented stimulus was identical to or a mirror image of a center standard stimulus. Reaction time and errors were measured. Previous mental rotation findings were replicated and the visual field variable produced significant effects for both dependent measures. An overall right visual field advantage was observed in the latency data, suggesting a left hemisphere superiority for at least one component process of the task. A significant interaction in the error data showed that alphanumerics produced less errors in the right visual field than in the left visual field, consistent with a left hemisphere superiority for processing verbal symbolic material. No such hemispheric difference in accuracy was found for unfamiliar characters.

Differential distraction effects in short-term and long-term retention of pictures and words.

Picture and word triads were followed by single visual and acoustic distraction tasks and by both tasks in sequence. Short-term retention between and within modalities differed as a function of type of distraction. Individual subject-recall probabilities for each single distraction condition failed to predict performance in the sequential dual-distraction conditions, underestimating performance for words and overestimating performance for pictures. A final delayed recall showed a reversal among distraction conditions within each modality, such that the best short-term retention condition (visual distraction) was poorest in long-term retention. However, long-term retentions of pictures was superior to that of words across all distraction conditions and irrespective of level of short-term retention. The results were interpreted in terms of separate acoustic and visual processing systems and the level of individual item processing within each system as a function of the type of interference originally expected.

Short-term retention of pictures and words as a function of type of distraction and length of delay interval.

Picture and word triads were tested in a Brown-Peterson short-term retention task at varying delay intervals (3, 10, or 30 sec) and under acoustic and simultaneous acoustic and visual distraction. Pictures were superior to words at all delay intervals under single acoustic distraction. Dual distraction consistently reduced picture retention while simultaneously facilitating word retention. The results were interpreted in terms of the dual coding hypothesis with modality-specific interference effects in the visual and acoustic processing systems. The differential effects of dual distraction were related to the introduction of visual interference and differential levels of functional acoustic interference across dual and single distraction tasks. The latter was supported by a constant 2/1 ratio in the backward counting rates of the acoustic vs. dual distraction tasks. The results further suggest that retention may not depend on total processing load of the distraction task, per se, but rather that processing load operates within modalities.

Process training derived from a computer simulation theory.

Kotovsky and Simon (1973) identified four basic subprocesses in their computer simulation of adult and adolescent performance on Thurstone letter series completion problems. In Experiment I, children from Grades 1 to 6 were pretested on those problems, and then experimental subjects were trained on two of the four processes as an attempt to experimentally support a correspondence between the computer subroutines and human cognitive processes. A posttest administered in the experimental and control conditions revealed a significantly greater improvement for experimental subjects, although both groups made significant gains. The children's distributions of errors were consistent with Kotovsky and Simon's predictions. In Experiment II, children from Grades 3 and 5 took four series completion tests without intervening training. The additional practice was sufficient for Grade 5 subjects to make improvements similar in magnitude to those produced by training. Grade 3 subjects, however, made no gains. These results are related to Tulving and Pearlstone's (1966) distinction between the availability and the accessibility of memory traces.

Coordinating cognitive information: task effects and individual differences in integrating information from several sources.

In many tasks people have to coordinate the information from several sources. An example would be driving a car while listening to directions. The driver has to establish a correspondence between a visual picture and verbal instructions. This paper addresses two questions concerning information coordination. Is there an ability to coordinate information received from several sources that is different from the ability to deal with information from each source, alone? Does coordination simply involve allocating resources to deal with the component tasks, or does the act of coordination itself constitute a separate task? Four experiments examined the coordination of a verbal component task with a visual-spatial and with an auditory component task. The results showed that the ability to coordinate perceptual and verbal information is separate from the ability to deal with either perceptual or verbal information, alone. A simple resource sharing model was not adequate in explaining how coordination occurred. We relate our results to a model in which perceptual reasoning occurs independently of verbal processing, but transforming perceptual information into a propositional form is affected by concurrent verbal processing.

Short-term retention of pictures and words: evidence for dual coding systems.

The recall of picture and word triads was examined in three experiments that manipulated the type of distraction in a Brown-Peterson short-term retention task. In all three experiments recall of pictures was superior to words under auditory distraction conditions. Visual distraction produced high performance levels with both types of stimuli, whereas combined auditory and visual distraction significantly reduced picture recall without further affecting word recall. The results were interpreted in terms of the dual coding hypothesis and indicated that pictures are encoded into separate visual and acoustic processing systems while words are primarily acoustically encoded.

Picture-word differences in decision latency: An analysis of single and dual memory models.

Semantic and perceptual size decision times for pictorial and verbal material were analyzed in the context of a unitary memory model and several dual memory models. Experiment 1 involved a same-different categorical judgment task. The results showed that picture-picture response latencies were 185 msec faster than the corresponding word-word latencies, and word-picture and picture-word latencies equaled the mean of these two extremes. Similarity of subcategory for "same" judgments led to faster decision latency for all presentation conditions. Additionally, a linear relationship was found between picture-picture and word-word latencies for individual item pairs. Experiment 2 involved a comparison of pictures and words across a. categorical judgment and a size judgment task. Pictures produced faster decision latencies in both tasks, and the latency diflerence between pictures and words was comparable across tasks. These data fit the predictions of a unitary memory model. Several variants of a dual memory model are rejected and those which fit the data require assumptions about storage and/or transfer time values which result in a functional regression to the unitary memory model.