The leftward cradling bias and prosody: an investigation of cradling preferences in the deaf community.

Popular theory on the tendency to cradle an infant to the left side points to the specialization of the right hemisphere for the perception and expression of emotion. J. S. Sieratzki and B. Woll (1996) recently suggested that more emphasis be placed on the auditory modality, specifically focusing on the role of prosodic information. In this study, the direction of the lateral cradling bias in a group of profoundly deaf children, a group of deaf adults, and a control group of adults with no hearing impairment was investigated. The authors found a strong leftward cradling bias in all groups, a bias that was, if anything, stronger in the deaf participants. Given that people who are profoundly deaf, especially those who have been deaf from birth, have not been exposed to auditory prosody, the data do not support the suggestion that such prosodic information is the basis for the leftward cradling bias.

The leftward cradling bias and hemispheric asymmetry for speech prosody.

Most women prefer to cradle an infant to the left side. It has been suggested that this bias is due to the specialisation of the right hemisphere for emotion, but investigations of visual asymmetries found no empirical support for this proposal. In a recent article, Sieratzki and Woll (1996) suggested that more emphasis should be placed on the auditory, rather than the visual, modality. Using a dichotic listening procedure we investigated whether ear preference for the perception of emotion in speech was related to the lateral cradling bias. Although the findings of both a leftward lateral cradling bias and a left ear emotion perception advantage were replicated, we found no association between the two variables--and thus fail to support the recent suggestions of a possible cause for the lateral cradling bias.

The analysis of drawing from memory performance in brain-damaged patients.

The drawing from memory task is frequently used in cognitive neuropsychology to investigate visual processing impairments. However, in surprising contrast to most other neuropsychological tests, the analyses of results on this task are most often based solely on qualitative judgements about the normality of a patient's performance. In most case reports, these judgements are not made with reference to normative data and are not made by individuals who are impartial with respect to the study (that is, using a blind rating procedure). There are several grounds for arguing that such analyses are inadequate. First, seemingly abnormal drawings made by a patient may well be within the range of performance shown by control subjects. Second, judgments that are not based on a blind rating procedure are likely to be influenced by knowledge about the patient's performance on other tasks. We describe an alternative assessment procedure that addresses both of these concerns.

Loss of stored knowledge of object structure: implications for "category-specific" deficits.

Following a right-hemisphere lesion, the patient SM had impaired object recognition, with good elementary visual abilities, and could derive information about object structure. He was also impaired on all tasks tapping stored structural knowledge, even when tested in the verbal modality. This suggests that SM has a disorder affecting stored knowledge of object structure, though he remains able to assemble novel structural descriptions. His object recognition ability also appeared significantly worse for non-living things. By contrast, existing models relating to stored knowledge would predict that SM would show greater impairment with living things. We argue that SM's deficit reflects the loss of a type of structural knowledge that relates to the "within-item structural diversity" of items. It is argued that living things show less structural variation than objects in the natural world, and might arguably be easier to recognise, because the image of the to-be-recognised object would be similar to the stored representation. Hence, a deficit affecting this aspect of stored knowledge would differentially impact upon non-living things. This argument receives confirming independent support from the finding that normal subjects ratings for the within-item structural diversity of visual stimuli are (unlike other "critical" variables) significant predictors of SM's naming performance.

Motor and perceptual factors in pseudoneglect.

An important variant of the traditional line bisection task has involved a mechanical device invented by Bisiach and his colleagues (Bisiach et al. Perceptual and premotor factors of unilateral neglect. Neurology 1990;40:1278-81 [3]). This tool was devised to dissociate motor from perceptual factors in hemi-spatial neglect, by means of a mid-line indicator which moved 'congruently' or 'non-congruently' with the direction of hand movement. In the non-congruent condition, Bisiach was able to demonstrate a reduction, or reversal, of the direction of bisection error in a number of patients with neglect. These errors were interpreted as instances of 'motor' neglect. Bisiach et al. [3] also tested 10 normal subjects, who did not differ on the two conditions of the task. However, the original experiment [3] required the use of the right hand only, and it has since become clear that bisection errors in normal subjects (i.e. pseudoneglect) are more substantial when dextral subjects use their left hands. By using a modified version of the Bisiach Tool we show that there is an effect of the motor versus perceptual condition on this task, but only when subjects use their non-dominant (left) hand.

Rotated drawing: the range of performance and anatomical correlates in a series of 16 patients.

Recently there has been interest in an unusual neuropsychological disorder in which the patient copies a complex drawing in a position which is grossly rotated relative to the original. This disorder is of interest partly because of its relationship to current theories of the process of object recognition, but the range of performances typically seen, as well as its anatomical correlates, remain obscure. We report 16 cases who produced grossly rotated drawings of the Rey and Taylor Complex Figures. These patients were drawn from an unselected series of 240 cases, with a wide variety of lesion types and sites. The performances of the 16 patients displayed striking similarities. We describe the formal features of these drawings and plot their anatomical correlates.

Visual determinants of the leftward cradling bias: a preliminary report.

A dominant leftward cradling bias is typically found in women in non-feeding interactions with infants. The present study investigated Manning and Chamberlain's (1991) claim that the perception of an infant, or doll, in the left visual field was critical for the establishment of this cradling preference. A leftward bias, of similar magnitude to that shown in previous studies, was shown in a sample of undergraduate female students when their left eye was not occluded, and in imagery. Unexpectedly, the cradling bias was not significantly affected by left eye occlusion. Paradoxically, a group of males, who showed no clear lateral bias, were strongly affected by eye occlusion. A strong leftward cradling bias was also found in the blind. These data do not support the suggestion (Manning & Chamberlain, 1991) that visual information is a primary determinant of the leftward cradling bias.

The neuropsychology of object constancy.

There have been several proposals for the mechanism by which we are able to recognize an object across a number of viewpoints. Viewpoint-dependent accounts suggest that recognition may be based on an incremental transformation (e.g., mental rotation) strategy, while a variety of viewpoint-independent mechanisms for object recognition have also been proposed. Recent research in neurobiology, based on the two cortical visual systems account, suggest that the processes of viewpoint-dependent and viewpoint-independent object recognition may rely on separate anatomical regions, and that brain lesions may leave patients with selective access to particular types of representation. Evidence from a variety of neuropsychological disorders are reviewed to support the position that viewpoint-independent object recognition depends upon the integrity of occipitotemporal structures. In addition, it is suggested that viewpoint-dependent processes (perhaps depending on occipitoparietal structures) may supplement this primary system under nonoptimal circumstances.

A double dissociation between knowledge of object identity and object orientation.

Two patients are reported who demonstrate the independence of knowledge of object identity and object orientation. One patient, with a visuo-spatial disorder, was unable to identify the upright canonical orientation for line drawings of objects, although she could correctly name the objects. A second patient, with visual object agnosia, was unable to name many objects, but could provide the upright canonical orientation--even for objects that he could not name. This double dissociation suggests that information about the canonical upright orientation of objects may be derived both from stored knowledge of objects, and 'directly' from visual information about object structure.

Agnosia for object orientation: implications for theories of object recognition.

Instances in which objects are copied accurately, but are dramatically rotated relative to the original, have been interpreted as evidence for viewpoint-independent accounts of the object recognition process. In two case reports, we demonstrate that patients who show rotation in copying also show difficulties in informing the examiner of the canonical orientation of known objects. In copying rotated versions of familiar objects, one subject showed a tendency to copy them in their canonical upright orientation, and both subjects copied non-representational line drawings with their principal axis vertically aligned, and with the irregular end pointing 'upwards'.

Neglect: mirror, mirror, on the wall--is the left side there at all?

Visuo-spatial neglect has long been thought of as a disorder of attention, but a recent experiment shows that, when images from the left side are reflected by a mirror into the 'good' hemispace, neglect patients behave as if the object were behind, or in, the mirror - as if the left side of their world did not 'exist'.

When is a view unusual? A single case study of orientation-dependent visual agnosia.

Several hypotheses have been proposed to explain why some neurological patients fail to recognise objects from unusual views: that it results from difficulty identifying an object's principal axis when it is foreshortened, identifying an object when landmark features are occluded, or an inability to rotate mental images. It was possible to test these hypotheses by examining the recognition abilities of a single case (A.S.), by using stimuli that were "unusual" only because of picture-plane misorientation. A.S. showed a recognition deficit in which his accuracy was proportional to the extent of misorientation from the normal upright for the object-although both principal axis and feature information remain visible after picture-plane rotation. Furthermore, A.S. performed with normal accuracy, and normal pattern of reaction time performance, on tasks of mental rotation. These findings suggest that none of these traditional accounts can adequately explain why this patient was unable to recognise objects from unusual views. These findings are discussed the light of recent suggestions of the basis of this type of disorder.

Recovery of object recognition in a case of simultanagnosia.

A case of visual agnosia is described. The patient, V C, complained of difficulties in identifying visual stimuli, after a stroke in the left occipital lobe. A neuropsychological examination demonstrated a range of symptoms consistent with (ventral) simultanagnosia, and a reaching disorder--suggesting Balint's syndrome. The patient's object recognition ability improved considerably over time.

Object recognition without knowledge of object orientation.

Several theories have been proposed to explain our ability to recognise objects from a number of viewpoints. Orientation-dependent accounts emphasize the position of the object relative to the viewer, while orientation-independent accounts (e.g. Marr) rely on descriptions of an object's component parts relative to its principal axis of elongation. An opportunity to compare the merit of these theories has arisen in a patient (L.G.) who had a rare neuropsychological sign in which knowledge of the canonical upright of object drawings was profoundly disrupted. Such orientation errors were evident in her drawings from memory and to copy, and in an orientation-matching task. In a critical experiment she showed a deficit in providing the canonical upright of individual object drawings that was independent of any difficulty in object recognition. The implications of these data for theories of object recognition are discussed.

Laterality of cradling in relation to perception and expression of facial affect.

A dominant leftward cradling bias has been observed in women in non feeding interaction with infants. Reasons for this behavior have been sought in behavioral asymmetries, but none have sufficiently justified the presence of this leftward pattern. Recently, the cradling bias has been linked to affective processing, considered to be a specialized function of the nondominant (right) hemisphere (Manning & Chamberlain, 1990). This study investigates Manning and Chamberlain's (1990) suggestions that a relationship exists between leftward cradling and the interpretation and expression of affect. Eighty-six nulliparous women were tested for this relationship by correlating direction of cradling bias with visual field dominance for perception of facially expressed emotion and expression of affect. No significant relationship was found to directly support the hypotheses.