Susanna Millar

Why does memory span improve with age? A review of the evidence for two current hypotheses

Abstract Evidence for two major hypotheses that attempt to explain the development in memory span with age is reviewed: the identification time hypothesis and the rehearsal hypothesis. The rehearsal hypothesis is also strongly related to the recent application of the working memory model to memory development. In this model, rehearsal is assumed to occur from an extremely young age. This assumption is critically evaluated. It is concluded that there is no strong support for the identification time hypothesis, except as a facet of familiarity. Neither was there good evidence that very young children use verbal rehearsal, although it did appear to be a factor later on. A revised model is proposed, based on three factors. The first is a speech perception system and phonological store; the second is a speech output system which can be used for sublexical segmentation and later rehearsal. The third system is long-term memory with links to both the speech perception and speech output systems. These links enable...

Memory span increase with age: A test of two hypotheses

Abstract Three experiments test the hypotheses that increase in memory span with age is determined by (i) identification time or (ii) articulation time. Experiment 1 matches 5- and 7-year-old children on the time taken to identify words given in a span test and finds that this does not equate span. Experiment 2 matches 5-and 7-year-old children on their articulation rates for individual words in a span test and finds that this is not sufficient to equate span performance. Experiment 3 matches 5- and 7-year-old children on their articulation rates for repeating a word three times and finds significant age effects in span scores for unfamiliar but not for familiar words. It is concluded that the developmental increase in span cannot be explained by differences in identification time, nor by the hypothesis that articulation time is the sole or major cause. It is argued that the development of span with age depends on a combination of factors which include familiarity and time to repeat a word more than once.

Models of Sensory Deprivation: The Nature/Nurture Dichotomy and Spatial Representation in the Blind:

It is argued that models of sensory deprivation often depend on a nativist versus empiricist dichotomy which has little basis in empirical fact. Fallacies about the nature of abilities and learning and about the interaction between sense modalities which follow from the dichotomy are examined in relation to explanations of spatial development in the blind. It is suggested that interactions between cognitive and perceptual factors need to be taken into account in order to explain the effects of sensory deprivation more adequately.

Symmetry in haptic and in visual shape perception

Four experiments tested the hypothesis that bilateral symmetry is an incidental encoding property in vision, but can also be elicited as an incidental effect in touch, provided that sufficient spatial reference information is available initially for haptic inputs to be organized spatially. Experiment 1 showed that symmetry facilitated processing in vision, even though the task required judgments of stimulus closure rather than the detection of symmetry. The same task and stimuli failed to show symmetry effects in tactual scanning by one finger (Experiment 2). Experiment 3 found facilitating effects for vertically symmetric open stimuli, although not for closed patterns, in two-forefinger exploration when the fore-fingers had previously been aligned to the body midaxis to provide body-centered spatial reference. The one-finger exploration condition again failed to show symmetry effects. Experiment 4 replicated the facilitating effects of symmetry for open symmetric shapes in tactual exploration by the two (previously aligned) forefingers. Closed shapes again showed no effect. Spatial-reference information, finger movements, and stimulus factors in shape perception by touch are discussed.

The Müller-Lyer illusion in touch and vision: implications for multisensory processes.

In six experiments, we used the Müller-Lyer illusion to investigate factors in the integration of touch, movement, and spatial cues in haptic shape perception, and in the similarity with the visual illusion. Latencies provided evidence against the hypothesis that scanning times explain the haptic illusion. Distinctive fin effects supported the hypothesis that cue distinctiveness contributes to the illusion, but showed also that it depends on modality-specific conditions, and is not the main factor. Allocentric cues from scanning an external frame (EF) did not reduce the haptic illusion. Scanning elicited downward movements and more negative errors for horizontal convergent figures and more positive errors for vertical divergent figures, suggesting a modality-specific movement effect. But the Müller-Lyer illusion was highly significant for both vertical and horizontal figures. By contrast, instructions to use body-centered reference and to ignore the fins reduced the haptic illusion for vertical figures in touch from 12.60% to 1.7%. In vision, without explicit egocentric reference, instructions to ignore fins did not reduce the illusion to near floor level, though external cues were present. But the visual illusion was reduced to the same level as in touch with instructions that included the use of body-centered cues. The new evidence shows that the same instructions reduced the Müller-Lyer illusion almost to zero in both vision and touch. It suggests that the similarity of the illusions is not fortuitous. The results on touch supported the hypothesis that body-centered spatial reference is involved in integrating inputs from touch and movement for accurate haptic shape perception. The finding that explicit egocentric reference had the same effect on vision suggests that it may be a common factor in the integration of disparate inputs from multisensory sources.

External and body-centered frames of reference in spatial memory: Evidence from touch

The study reports independent effects of external and body-centered reference cues on spatial coding of an irregular sequence of haptic locations. The aim was to investigate the nature of spatial coding by using a modality that does not provide distal cues routinely. Our method isolates and combines body-centered and external spatial reference cues for irregularly placed locations, scanned along a raised-line route. Disrupting body-centered reference for the locations, by orienting the map differently to the body in the test phase than in the presentation phase, doubled errors in positioning the locations along the route in recall. Adding external reference, by giving instructions to use a surrounding frame for reference when body-centered coding was disrupted, reduced errors to near baseline (no-rotation) levels. Adding external reference cues to intact (not displaced) body-centered reference halved errors, as compared with the baseline. The results are consistent with the hypothesis that accurate spatial coding is determined by the congruence of potential reference cues from diverse sources. The new findings suggest that external and body-centered reference cues have independent additive effects on spatial coding. The sequence of locations had a significant effect in all the reference conditions, suggesting the additional use of fortuitous but distinctive local touch cues on the route. The discussion considers theoretical and practical implications of the results.

SPATIAL REPRESENTATION BY BLIND AND SIGHTED CHILDREN

The problem I want to consider is how the mode and level of experience affects children’s spatial thinking. To the non-psychologist spatial and visual experience are almost synonymous. Congenitally and early blind children lack such experience. Of course, other sense modalities also provide spatial information. We can, for instance, locate sounds, although this is not always very accurate; and hearing does not inform us about physical expanse, planes and surfaces. But this information can be derived from touch and movement as well as from vision. Some major theories of children’s spatial representation regard the source of information as largely irrelevant. For instance, Gibson (1969) assumes that spatial representation depends upon the progressive detection of invariant amodal features and relations in the external world. Piaget’s (1956, 1971) view is very different. He considers the process one of intellectual construction, derived from internalized sensori-motor activity. It is not perhaps entirely accidental that the bulk of Eleanor Gibson’s work is concerned with vision; while initial evidence for Piaget’s view depended more on observations on active touch.

Self-Referent and Movement Cues in Coding Spatial Location by Blind and Sighted Children

The study tested the hypothesis that movement and self-referent information differ, and that children can use both to code unseen locations. In one experiment blindfolded sighted children made more errors with changed than with unchanged accessing movements, despite unchanged reference conditions. Rotation decreased accuracy further, although most responses were to the correct side. Age did not interact with experimental conditions. In another experiment blind children and matched blindfolded controls were less accurate with changed movements; and rotations were more difficult still. Visual experience, but not age, interacted with conditions. The blind showed significantly more self-reference (responses to the original side in rotations), and were somewhat worse also with changed movements alone but did not differ from controls when movements and references were unchanged. The results support the hypothesis that movement and self-referent information differ. Visuospatial experience and task conditions rather than age seem to determine the extent to which children use either form of information.

Visual Experience or Translation Rules? Drawing the Human Figure by Blind and Sighted Children

Figure drawings by 30 blind and 30 sighted children, tested under blindfold and visual conditions, were compared on positioning and drawing scores. Results showed that the majority of the blind, unlike the sighted made positioning errors, and were unaware of the correct placement rule. The older blind did not differ from the sighted on figure drawing, but the younger blind scored significantly worse. Blindfolded compared to visual conditions produced decrements mainly on cohesion and amount of detail by the sighted. The findings suggest that drawing depends on the acquisition of translation rules for which prior visual experience is a facilitating but not a necessary condition. The absence of visual feedback during drawing seems to have detrimental effects mainly on the articulation of drawing.

The Utilization of External and Movement Cues in Simple Spatial Tasks by Blind and Sighted Children

The role of visual experience in coding spatial position by movements or by external cues was examined in simple (nonrotational) shift tasks with blind and sighted children. Age and the salience of external cues were also of interest. Results showed that the congenitally totally blind used movement cues significantly more even when external cues were present and prominent. The blind with minimal visual experience coded by external cues, but made errors beyond the age by which blindfolded sighted children performed correctly. It was argued that visual experience affects coding by drawing attention to external cues, and by providing more adequate spatial information than other sources usually available to the blind. In its absence, movement coding and self-reference can become preferred strategies.