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Biomedical subjects

N C Nettleton

Publications and source records attributed to N C Nettleton.

At least 37 records · Page 2Linked to original sources
PubMed1985

Mirror reading in right and left handers: are sinistrals really superior?

While left handers, where they do in fact appear to differ from right handers in cognitive function, have generally been found to be slightly inferior on verbal tasks, there are some reports of a sinistral superiority for nonverbal or spatial abilities. Tankle and Heilman (Brain and Language, 1982, 17, 124-132) report a sinistral superiority in (obligatory) reading of left-right mirror-reversed text. However, in an investigation which included various other forms of geometrical transformation of the written word, we find that strong familial sinistrals are either not different from or even slightly inferior to dextrals in reading most transformations, including left-right mirror reversals.

Adolescent↗
PubMed1984

A moving video window or a mask yoked to eye movements: experiments on letters, words and biological movement with prolonged hemifield stimulation.

We describe the first use of a new technique, which permits prolonged presentation to one or other visual field of complex, realistic, "ecologically valid" stimuli. An infrared eye movement transducer is linked to a visual display such that an electronic mask (of adjustable dimensions) or, alternatively, a "window" can be made to move as consequence of eye movements. The mask can be made to move exactly with the initiating eye movement, or with positive gain, or in the opposite direction (with or without gain), or in both directions simultaneously ("scissoring"). Alternatively, the apparatus can be set to blank the entire display should an eye movement occur with an excursion greater than a preset criterion level. The display itself can be either computer generated or can consist of a pre-recorded video film. We report preliminary findings with this apparatus. When subjects detected a letter target in a three-by-three letter matrix of laterally presented letters, exposure durations from 50 msec to 400 msec showed consistent right visual field (RVF) superiorities. (Nor was there any evidence of left visual-field, LVF, superiorities at very brief exposures as others have claimed.) Equally strong RVF superiorities also appeared when subjects decided whether or not two simultaneously and laterally presented (for 500 msec) words rhymed, the word pairs being phonologically and orthographically similar (DOWN-GOWN), phonologically similar and orthographically distinct (FARE-HAIR), phonologically distinct and orthographically similar (MOWN-DOWN), or both phonologically and orthographically distinct (FORT-GOAT). Finally, Johansson's (1973, 1976) biological movement procedure was adapted for lateral viewing, with unlimited exposure times. However, the predicted LVF superiority did not eventuate, when subjects decided whether moving points of light, attached to the limbs of darkened walkers, were worn by males or females. Further possible applications of this technique are described for normal and clinical subjects.

Eye Movements↗
PubMed1983

Head and body space to left and right, front and rear--I. Unidirectional competitive auditory stimulation.

Very substantial right ear advantages (REAs) and right side advantages (RSAs) are reported for vocal shadowing latencies to laterally presented competitive verbal stimuli from a single earphone or loudspeaker. When head and body hemispace were dissociated by inducing a 90 degree head turn, with presentations either lateral or front-back with respect to the body, RSAs and REAs vanished, indicating that stimuli neither in the head nor in the body hemispace alone appear capable of generating any lateral asymmetries. However, a front-of-body (but not front-of-head) superiority compared with the rear was obtained. Most importantly, a powerful ventriloquism effect was obtained whereby a laterally placed dummy loudspeaker produced "pseudo"-RSAs with anterior-posterior-located sound sources. This suggests that it is the perceived position of a sound source rather than its actual position or ear of entry which determines asymmetries.

Auditory Perception↗
PubMed1983

Head and body space to left and right, front and rear--II. Visuotactual and kinesthetic studies and left-side underestimation.

We report seven experiments involving unimanual or bimanual tactual or visuotactual judgments with horizontally or vertically disposed rods, performed in left or right hemispace, in the context of Bowers and Heilman's (Neuropsychologia 18, 491-498, 1980) hemispace hypothesis. We were only able to weakly confirm their finding of a left hemispace superiority, though either hand was more accurate when in its own hemispace. However, their observation of a left pseudoneglect phenomenon was supported and extended: we found that the left hand underestimates relative to the right, and that there may be left hemispace underestimation which is lost with 90 degree head turns, when horizontal extents are underestimated in the direction of the head turn.

Cerebral Cortex↗
PubMed1983

Name and face matching in one or two visual fields: a test of models of hemispheric specialization.

In two experiments a name and a face (each male or female) were simultaneously flashed to either the same or opposite visual fields (left or right), for matching congruent (same sex) or incongruent (opposite sex), to test the predictions of various models of hemispheric specialization. While overall best performance occurred with a face in the left visual field (LVF) and a name in the right visual field (RVF), and worst with the opposite configuration, the general pattern of results was incompatible with either a direct access model or an activational/attentional account. The results were, however, most compatible with the predictions of a semispecialized hemispheres account, whereby cerebral asymmetries are seen as relative rather than absolute, either hemisphere being capable of processing either kind of material (verbal or visuospatial), but to different levels of efficiency. However, despite the fact that the stimulus materials had previously been shown to produce stable and consistent lateral asymmetries in the predicted directions when presented in isolation, in the composite, integrative matching task the position of the name seemed to be the major determinant of the resultant asymmetries. It would seem therefore that when such stimuli are to be cross matched, either left hemisphere (language) processes somehow dominate right hemisphere (visuospatial) processing (though not in the way that would be predicted by a simple activational/attentional account) or the left hemisphere's greater capacity predominates.

Discrimination Learning↗
PubMed1983

An unexpected interactive pattern of visual field asymmetries revealed by faster/slower response partitioning.

Subjects were presented with unilaterally-exposed schematic, outline faces in one condition, and three-letter single-syllable first names in another. In either case there was an ensemble of four items which were to be partitioned, by the subjects making a manual choice-reaction-time response, into two subsets. No easy rule permitted the partitioning either of the faces or of the names (DEN, LES versus LEN, DES). While no clear pattern of asymmetries emerged from an overall analysis, or from a simple comparison of the two types of response, when the subjects' individual responses were instead partitioned into faster and slower, a striking pattern of interactive asymmetries emerged which was consistent for both sexes and both tasks. Thus the slower of the two responses was associated with a left field superiority, and the faster with a right. These findings were discussed in the context of perceived or covert task demands, which are not always immediately recognizable from a superficial or conventional analysis of response data, and the effect of positive (target) and negative (nontarget) processing upon behavioral asymmetries.

Discrimination Learning↗
PubMed1983

Head and body hemispace to left and right III: Vibrotactile stimulation and sensory and motor components.

Response latencies were measured to vibrotactile stimulation delivered to the forefingers of the left or right hands which were positioned ipsilaterally or contralaterally (across the midline) in left or right hemispace. While the two hands did not differ in speed of response, either hand performed better when located in right hemispace (experiment 1). This effect was greatly reduced, though not eliminated, with 90 degrees lateral head turn, when performance was better with stimulation and responding in right-of-head hemispace, but not right-of-body hemispace (experiment 2). When different hands received stimulation and initiated responses, and were located in either the same or opposite hemispace, right-hemispace superiority was found to be motor rather than sensory (experiment 3). These findings are discussed in the context of the true and the phenomenological midline and the clinical syndrome of hemineglect.

Adult↗
PubMed1983

The effects of task, practice and sequencing upon the lateralization of semantic decisions.

We report three reaction time experiments in which first names were laterally presented and subjects made discriminatory manual or vocal responses (male/female), or named the stimuli, or judged whether name pairs were of same or opposite sex. The experiments addressed the issue of whether the strength and direction of laterality effects changed with practice and/or stimulus repetition. Performance facilitation with a repeated stimulus was greater when the same rather than the opposite hemisphere received the repeated stimulus, indicating that the effects of stimulus repetition are partly hemisphere-specific. Task practice was found to be a far more important determinant of changing asymmetries than stimulus repetition; however such practice may decrease as well as increase lateral asymmetries. These effects did not extend to the situation where a task was preceded by another of quite a different nature--name before face processing, and vice versa. We conclude that sequencing and practice effects are important but complex determinants of the direction and magnitude of lateral asymmetries, indicating that lateral asymmetries are labile rather than fixed and reflect relative rather than absolute specialization in interhemispheric processing capacity.

Decision Making↗
PubMed1983

The lateralization of arithmetic and number processing: a review.

Calculation and number processing require ideographic and semantic operations which may involve the right as well as the left hemisphere. There is often also present a spatial component, whether overt as with column-addition or multiplication procedures, or covert if numbers are recoded into continuously varying analog quantities or magnitudes of a psychophysical or imaginal nature, to facilitate numerical comparison. Again right hemisphere mechanisms may be partly responsible. Evidence for such a minor hemisphere contribution is reviewed in the light of studies with clinical and commissurotomy cases, and normal subjects. Calculation itself is hard to define, as it often seems to reduce to the operation of overlearn, associative, tabular look-up functions and algorithms. Indeed alphabetic comparisons analogous to numerical tasks should generate similar laterality effects in clinical and normal populations.

Brain Damage, Chronic↗
PubMed1982

Braille reading and left and right hemispace.

Twelve blind adults were timed in locating phonologically and semantically defined targets in Braille lists. The "reading" hand was placed either out from or across the body, i.e. in ipsilateral or contralateral hemispace. Despite strong and consistent, if idiosyncratic, hand superiorities for all types of list, contrary to two previous reports there was no evidence of either a general left-hand preference or an overall left-hand superiority. Moreover neither the magnitude nor the direction of hand superiorities changed when hands were tested in contralateral hemispace. At least this complex continuous task, hemisphere-hand connections appear more important than hemisphere-hemispace relationships. Left-hand (or left-hemispace) superiorities in tactual tasks of a verbal nature may only occur with novel, unfamiliar or perceptually degraded materials.

Adult↗
PubMed1980

Left handedness, birth order and birth stress.

The handedness of 942 subjects (305 tertiary students, 591 of their siblings and 46 of their children) was ascertained by a 14-item questionnaire. The mothers of the subjects supplied information about maternal age at birth, birth weight and the presence or absence of twelve conditions likely to be associated with birth stress for each subject. No increase in left handedness was found among fourth or later born children. A significant decrease occurred in first-borns of both sexes, although these had more stressful births than the other subjects. No relationship between maternal age, birth weight or reported birth stress and left handedness was found. Thus the hypothesis that birth stress is a major cause of left handedness in normal subjects was not supported. Acknowledgements. We are particularly grateful to the students from the Institute for Early Childhood Development and their families, who provided the data for this study. We also wish to thank Dr John L. Bradshaw for his very constructive comments during the preparation of this paper.

Adolescent↗