Left Bias Research Articles

A Left Attentional Bias in Chronic Neglect: A Case Study Using Temporal Order Judgments

Previous studies of left visuospatial neglect using temporal order judgments (TOJs) have reported a temporal advantage for a stimulus presented on the right of fixation. The present case study examines an individual who shows a left temporal advantage on TOJ tasks, despite classic left-sided neglect on other tasks and in self-report. Experiment 1 found a continued left advantage on TOJs when employing a novel red/blue TOJ task to reduce potential response bias. Phasic alerting tones presented prior to random trials in Experiment 2 did not improve the abnormal attentional bias, as has been reported in previous studies of neglect. The addition of unilateral trials mixed within bilateral trials in Experiment 3 reduced the observed left advantage, suggesting a flexible attentional focus and implicating a role for strategic endogenous attentional strategies in this individual. Some implications for our understanding of endogenous orienting and relevance to rehabilitation therapy are discussed.

LATERAL AND VERTICAL ATTENTIONAL BIASES IN NORMAL INDIVIDUALS

Background: When normal people attempt to bisect lines they often make their mark to the left of midline (pseudoneglect) and when attempting to bisect radial lines normal people tend to bisect distal to the actual midline. These biases might be related to asymmetrical activation induced by making spatial computations or attention-intentional preferences. The purpose of this study was to learn if in the absence of spatial computations normal subjects would demonstrate a left and upward bias. Methods: Normal subjects (139) were given 8 pegs and asked to place these pegs anywhere on a 2-foot-square board. Results: Overall, the subjects displaced the pegs to the left and upward. Conclusions: The overall left-distal bias observed in this experiment was not induced by spatial computation or misperceptions, but is consistent with the postulate that the right hemisphere is dominant for attention-intention and has a relatively distal bias.

Perceptual Asymmetry for Chimeric Faces and Winter Disturbances in Mood and Behavior

Abstract. Different affective disturbances are related to brain activity, and, thus, to perceptual bias in very specific ways ( Keller et al., 2000 ). During the winter months, approximately 90% of people report lowered levels of mood and increased levels of anxiety to varying degrees (e.g., Magnusson, 2000 ). The current study examines the relationship between such winter mood disturbances and perceptual asymmetry on the chimeric-face task using a nonclinical sample (38 males and 92 females). Because of the suggested influence of symbolic light on cognitive processing of seasonal depressives ( Bouhuys, Meesters, Jansen, & Bloem, 1994 ), chimeric faces were presented on both symbolic bright and dark backgrounds. Face processing demonstrated the expected left hemifacial perceptual bias. However, the magnitude of individuals' perceptual bias bore no relation to subjectively reported seasonality, depressed mood, or anxiety. This was regardless of whether the faces were displayed on symbolic bright or dark backgrounds. Methodological factors must be considered. However, results are discussed in terms of the importance of clarifying the distinct nature of the psychological and neurobiological profile associated with winter disturbances in mood, and the possible influences of symbolic light on cognitive processing.

Directional asymmetry of pelvic vestiges in threespine stickleback

Extensive reduction of the size and complexity of the pelvic skeleton (i.e., pelvic reduction) has evolved repeatedly in Gasterosteus aculeatus. Asymmetrical pelvic vestiges tend to be larger on the left side (i.e., left biased) in populations studied previously. Loss of Pitx1 expression is associated with pelvic reduction in G. aculeatus, and pelvic reduction maps to the Pitx1 locus. Pitx1 knockouts in mice have reduced hind limbs, but the left limb is larger. Thus left-biased directional asymmetry of stickleback pelvic vestiges may indicate the involvement of Pitx1 in pelvic reduction. We examined 6,356 specimens from 27 Cook Inlet populations of G. aculeatus with extensive pelvic reduction. Samples from 20 populations exhibit the left bias in asymmetrical pelvic vestiges expected if Pitx1 is involved, and three have a slight, non-significant left bias. However, samples from three populations have a significant right bias, and one large sample from another population has equal frequencies of specimens with larger vestiges on the left or right side. A sample of fossil threespine stickleback also has significantly left-biased pelvic vestiges. These results suggest that silencing of Pitx1 or the developmental pathway in which it functions in the pelvis is the usual cause of pelvic reduction in most Cook Inlet populations of G. aculeatu, and that it caused pelvic reduction at least 10 million years ago in a stickleback population. A different developmental genetic mechanism is implicated for three populations with right-biased pelvic vestiges and for the population without directional asymmetry.

Dépression, alexithymie et latéralisation dans la façon de porter un nouveau-né

Several authors have reported that participants had a leftward bias when holding a new-born or a young infant. Recent studies showed that a right hemispheric specialization in the recognition of facial expressions was linked to this bias. In addition, there is some evidence that depressed mothers expressed a significant decrease in this left holding bias. Other investigators demonstrated that people suffering from depression or alexithymia could present a dysfunction of the right cerebral hemisphere. Our study was conducted in two maternity hospitals on a sample of 148 mothers and was aimed at exploring whether depression, alexithymia or other factors (e.g., newborns’ weight or sex) were related to biases expressed by mothers when they held their new-born. Four questionnaires were used: 1) an infant holding questionnaire; 2) Nine items from the Edinburgh Handedness Inventory; 3) The twenty-item Toronto Alexithymia Scale-1 (TAS 20) questionnaire; 4) The CES-D Scale for depression. In addition, information concerning the mother and the newborn was collected (the age of the mother and of the newborn, the gender of the infant, the infant’s birth weight, etc.). Our results showed: 1) that mothers displayed a significant leftward (68%) holding bias; 2) that depressed mothers tended to hold their new-born on the right side. Moreover, these latter mothers displayed a different holding posture compared to non-depressed mothers. More specifically, mothers evaluated as non-depressed carried their infant predominantly (70%) in the typical cradling posture (arm-holding), whereas mothers evaluated as depressed alternated arm-holding with shoulder-holding postures. In addition, our study showed a relation between the low new-born’s weight (3 kg or less) and holding biases, but only for male infants. These results confirm previous findings from our group and from other researchers of a significant left bias for holding a new-born in a population of new mothers. The findings of relationships between infant holding biases, holding patters and depression levels suggest that maternal anxiety and/or depression can affect holding biases.

Effects of biasing the location of stimulus presentation, and the muscarinic cholinergic receptor antagonist scopolamine, on performance of a 5-choice serial reaction time attention task in rats

A major purpose of the present studies was to determine the effects of varying the relative frequency, or bias, of stimulus presentation at different locations in a five-choice serial reaction time attention task. Training sessions were conducted in which the stimulus duration was held constant at 2 s and, initially, stimuli were presented with equal probability above each of the levers. During testing sessions, however, stimulus duration was either 0.2 or 2 s, and the frequency of presentation was varied among no bias, a middle bias, a left bias or a right bias condition. The training conditions were then changed such that the frequency of presentation was always a left bias, and test sessions were again conducted with no, middle, left or right bias. In the presence of the 0.2-s, but not the 2.0-s, stimulus, the percentage of correct responding on each of the choice levers during test sessions varied directly with the bias conditions in that the percentage of correct responding was highest at the most frequently presented location and lowest at the least frequently presented location. In addition, scopolamine, but not metscopolamine, increased omissions while also increasing anticipatory responses in rats trained under left-bias conditions and tested under right-bias conditions. The present findings suggest that varying the frequency of stimulus location can provide additional measures of attention in the five-choice serial reaction time task.

Perceptual asymmetry for chimeric stimuli in children with early unilateral brain damage

The present study used a chimeric stimuli task to assess the magnitude of the left-hemispace bias in children with congenital unilateral brain damage ( n = 46) as compared to typically developing matched controls ( n = 46). As would be expected, controls exhibited a significant left-hemispace bias. In the presence of left hemisphere (LH) damage, the left-hemispace preference was found to be present, but attenuated, whereas right hemisphere (RH) damage resulted in a less lateralized process. Examination of lesion severity revealed that large lesions in the RH were associated with a reversal of the typical left-hemispace bias, while small lesions resulted in a left bias approximating that of controls. In contrast, the left-hemispace preference in children with LH damage was similar across lesion size. We conclude that damage to either hemisphere early in brain development may alter hemispheric preference for processing of nonverbal stimuli, and that at least in the case of RH damage, alteration of the normal perceptual asymmetry may depend on the interaction between lesion side and severity.

Reach and posture hand preferences during arboreal feeding in sifakas (Propithecus sp.): A test of the postural origins theory of behavioral lateralization.

Sixteen sifakas (11 Propithecus verreauxi coquereli, 2 Propithecus verreauxi verreauxi form majori, and 3 Propithecus tattersalli) were videotaped as they fed on leaves in an arboreal context. The hand used to feed and the hand used to maintain postural stability was coded. For each subject, the lateral bias of the hand used to feed was opposite the hand used in postural support. Seven sifakas displayed no bias for feeding or posture-related hand use, 7 sifakas displayed significant feeding-related reach preferences for pulling branches to the mouth (5 left- and 2 right-hand preferences), and 9 sifakas exhibited significant hand preferences for postural support (2 left-, 7 right-hand preferent). Although these data do not strongly support the postural origins theory of behavioral lateralization, the modal preference pattern for sifakas that displayed significant hand preferences for posture and feeding involve a left bias for feeding and a right bias for postural support. s reserved).

Ground scratching and preferred leg use in domestic chicks: Changes in motor control in the first two weeks post-hatching

Lateralisation of a variety of visual functions: food discrimination, fear response, copulation, and performance of topographical and other tasks, such as olfactory and auditory functions, have been described in the domestic chick, Gallus gallus domesticus. A bias to left hemisphere control on day 8 and to the right on day 11 has also been demonstrated in the domestic chick. In this study we show that motor control as to foot preference in initiating a scratching bout and a tape-removing task is lateralised in both adults and chicks. There was a preference for the right leg to initiate a bout of ground scratching in both male and female adult birds. Second, foot preference is also affected by the changes in shifts of bias on day 8 and day 11. The right leg preference in initiating a ground scratching bout observed on day 5 is reversed to a left leg preference on day 8. This then reverts to the right leg preference after day 11. Hence it is postulated that the hemisphere that is not activated due to the bias of age controls the first leg to be used in initiating routine movements such as ground scratching. For the tape-removing task the right leg was used to remove a tape adhered to the beak of the chick for the trained group on day 8; but there was no preference in the naïve group. Similarly, on day 11 a left foot bias was observed for the trained group and right foot bias for the naïve group. To remove a tape the activated hemisphere on days of bias is used; whereas in a novel situation the foot use is reversed. Thus, footedness is affected by age, type of task, and changing hemispheric dominance.

Sex differences in line bisection as a function of hand

If subjects are asked to indicate the midpoint of a horizontal line, they tend to bisect it left of the center, a phenomenon called ‘pseudoneglect’. Assuming that this task evokes visuospatial processes, the left bias is generally considered to arise from a right-hemispheric activation. Numerous factors affect pseudoneglect. Although, only few studies have examined the influence of sex in visual line bisection, most of theses studies reported no significant main effect of sex. Possible interactions between sex and other performance factors that are linked to the motor component of this task, e.g. hand use, are rarely examined. We studied the interaction of these two variables using right-handed females and males in a line bisection task. The results clearly indicate that hand use and sex interact, with females showing the left bias to a similar extent with both hands while males show the bias predominantly with the left hand. Moreover, the position of the lines (left, middle and right) significantly affect left bias in visual line bisection and interact with hand use. It is hypothesized that the larger cross-section of the posterior corpus callosum in females enables a stronger interhemispheric connectivity of visuospatial cortical areas resulting in a strong left-sided bias in hand motor cortical areas of both hemispheres. In males, motor cortical activation would accordingly be mainly restricted to the right hemisphere.

Abnormal line bisection judgements in children with Tourette's syndrome

Tourette's syndrome (TS) has been associated with loss of normal basal ganglia asymmetry, as well as loss of normal functional asymmetry, including the leftward bias on traditional visuospatial tasks such as line bisection and turning bias tests. The aim of the present study was to examine the lateralisation of visuospatial attention in TS. We examined the effect of an irrelevant moving-dot background on line bisection judgements. Nine children with a DSM IV diagnosis of TS participated, in addition to 9 healthy controls, individually matched for age, sex and IQ. Horizontal lines of varying length were presented on a computer screen with either a blank background, or a moving, random-dot field. The dots moved either leftward or rightward across the screen at 40 or 80 mm/s, and participants were instructed to ignore these distracting stimuli when judging the lines. TS children were found to be abnormally right-biased in line bisection in a similar fashion to unmedicated ADHD children who, in a previous study, showed a similar small, yet significant, right-bias in line bisection. Matched controls showed a small, nonsignificant left bias, consistent with past research. Unlike previous findings with hemineglect patients, the irrelevant moving background had no effect on bisection performance for TS children or healthy controls. The present findings suggest a deficit in visuospatial attention consistent with the emerging picture of a lateralised dysfunction of frontostriatal circuitry in TS.

Patterns of hemispheric perceptual asymmetries: left hemispatial biases predict changes in anxiety and positive affect in undergraduate women.

Consistent with the tripartite model of anxiety and depression, hemispheric asymmetries may be differentially associated with depressive and anxious symptoms. Indeed, research has demonstrated that asymmetries do exist when examining hemispatial biases in both anxious and depressed individuals; however, the magnitude and direction of these asymmetries has been variable. The Chimeric Faces Task was used here to measure these asymmetries, along with measures for current and future levels of anxiety and depression. Results indicated that (a) increased left hemispatial biases at Time 1 predict increased anxiety (i.e., physiological hyperarousal) at Time 2 among female undergraduate students and (b) decreased left hemispatial biases at Time 1 predict decreased positive affectivity at Time 2 among the same participants. The possibility that hemispatial biases represent a vulnerability to future anxiety and depression is discussed.

Evidence of schizophrenia patients' reduced perceptual biases in response to emotion chimera.

The goal of the study was to determine whether dextral individuals with schizophrenia display atypical perceptual biases in response to faces in general, or whether they display atypical perceptual biases in response to emotional facial cues. To this end, we assessed perceptual processing in schizophrenia patients with four types of free-vision chimeric stimuli. Perceptual biases were evaluated in 45 schizophrenia patients and in 46 controls using two face (emotion, gender) tasks and two nonface (dots, gradients) tasks. In response to the emotion chimera, the patients with schizophrenia displayed a reduced left perceptual bias. The two groups did not differ significantly in their response to the gender chimera or to the two nonface chimera. These findings are consistent with the assertion that schizophrenia patients have impaired emotional perception. In the discussion we consider possible reasons for schizophrenia patients' difficulty comprehending emotional facial stimuli. We suggest that schizophrenia patients' reduced perceptual bias in response to the emotion chimera reflects a hypothesized affective information-processing deficit.

Patterns of hemispheric perceptual asymmetries: Left hemispatial biases predict changes in anxiety and positive affect in undergraduate women.

Patterns of hemispheric perceptual asymmetries: Left hemispatial biases predict changes in anxiety and positive affect in undergraduate women.

Language laterality in English/Welsh bilinguals: Language-acquisitional and language-specific factors in the development of lateralisation

In order to test the hypothesis that monolinguals differ from bilinguals in their pattern of language lateralisation and to examine the relative merits of language-acquisitional versus language-specific factors, two experiments involving divided screen presentation of two languages were conducted using Welsh/English speaking participants. In the first experiment 80 monolingual teenagers were compared to 80 bilingual teenagers on a tachistoscopic "visual half-field" test of Welsh and English nouns and verbs. ANOVA revealed a greater left hemisphere advantage for Welsh-English bilinguals as compared to English monolinguals. Thus, in contrast to previous studies, in our bilinguals there was evidence of greater left hemisphere involvement in the processing of language. In the second experiment, four separate groups of 40 teenagers, varying in the age and manner of acquisition of their languages, were compared on the same test of Welsh and English words. These groups can be viewed as graded from the early to late bilinguals. ANOVA revealed a greater left hemisphere advantage when processing Welsh as compared to English words for all four groups. However no significant difference was observed between the four groups in respect of laterality for Welsh and English, indicating an equally greater left hemisphere bias for all four groups when processing Welsh words. We discuss these results in terms of a language-specific effect and suggest the specific orthography of the Welsh language (for individually presented nouns and verbs) promotes a left hemisphere advantage over and above language-acquisitional factors.

Left Hand Preferences in Capuchins (Cebus apella): Role of Spatial Demands in Manual Activity

Sixteen capuchins (Cebus apella) participated in four tasks that differed in their exploration demands and availability of visual cues. The two explorative tasks required the monkeys to discover sunflower seeds hidden in crevices in objects of various shapes, with vision (Haptic-Visual task) or without vision (Haptic task). Two other tasks required the capuchins to grasp sunflower seeds directly on a flat support, with vision (Visual reaching) or without vision (Tactual reaching). The presence or absence of exploration demands had a significant effect on the direction of hand preferences. The group displayed greater left hand preferences for the Haptic and Haptic-Visual tasks than for the two reaching tasks. The strength of manual preferences did not differ significantly among the four tasks. These findings suggest that the manipulo-spatial demands of a task are of particular importance for the expression of left hand bias in a population of capuchins. It is argued that left hand preferences for the haptic tasks may reflect a right hemisphere specialisation to integrate the spatial and motor components of action.

Processing and recognition of facial affect in schizophrenia.

A deficit in the recognition of facial affect has been well documented in people with schizophrenia. Our 1995 research with normal subjects showed that hemispheric bias for processing facial affect is related to accuracy of recognition of facial affect. We tested whether this relationship holds in a sample of 25 people with schizophrenia who completed tasks of identification of facial affect and chimeric facial affect. Subjects with a left visual-field bias were significantly more accurate in identifying one facial emotion (sad) than were other subjects. Individual differences in hemispheric advantage for processing affect appears to be an important variable related to functional brain capacity within different populations.

Neonatal neurobehavioral correlates of lateral bias and affect in infant chimpanzees (pan troglodytes)

In this study, I extend previous findings of population‐level asymmetries in lateral bias of multiple behavioral measures in infant chimpanzees. Moreover, I propose that different neurobehavioral mechanisms are associated with different behavioral measures. A longitudinal design was employed to assess neonatal neurobehavioral integrity, lateral bias at 3 months old, and lateral bias and affect at 9 to 10 months old. Approximately half of the sample was raised under standard nursery conditions (females, n = 9; males, n = 11), and the other half was raised in a “responsive care” nursery designed to promote species‐typical chimpanzee development (females, n = 9; males, n = 8). Significant right biases were confirmed for hand‐to‐mouth self‐calming behavior. Significant left biases were found in grasping of objects (at 9–10 months old). Hand‐to‐hand grasping, reflexive stepping, head posture while sleeping in a supine position, and defensive swipes were individually lateralized rather than population level biased. Neonatal neurobehavioral assessments were found to be significantly associated with lateral bias both at 3 months and at 9 to 10 months old. Arousal at 2 days of age was negatively correlated with hand‐to‐mouth bias, motor performance at 2 days old was positively correlated with hand‐to‐hand bias, and orientation performance at 30 days of age was positively correlated with head bias. The lateral bias in touching and grasping objects at 9 to 10 months of age was positively correlated with head bias by 3 months of age and with State Regulation at 2 days of age. Affective behavior at 9 to 10 months old was correlated with defensive bias at 3 months and with muscle tone at 2 days of age. Rearing environment, gender, and emotional reactivity were found to influence lateral bias. These findings support the hypothesis that different asymmetric behaviors, even if lateralized to the same direction, may reflect different biological processes and different functional mechanisms.

Affect identification bias demonstrated with individual chimeric faces.

The current study extends previous findings of a left visual-field bias in chimeric face tasks, by using a new procedure which incorporates chimeric stimuli depicting both positive and negative target affects and requires the identification of affect in individually presented faces. This new procedure is more representative of the types of judgements made in daily social interaction. Results with this new procedure are consistent with previous findings, indicating a significant left visual-field bias for both positive and negative affects in the majority of subjects. Handedness was significantly related to lateralization scores, with dextrals showing greater left visual-field biases than sinistrals. Among sinistrals, a left visual-field bias was noted only for happy chimera.

Footedness in foraging muskoxen Ovibos moschatus

Authors investigated the propensity for the wild muskoxen Ovibos moschatus (Zimmerman, 1780) to exhibit right or left bias in foreleg use while foraging during winter. Authors found little evidence of such leterlisation, either on the individual or population level. Only 3 of 40 animals exhibited significant right- or left-footedness, and the distribution across the population for use of either limb was near 50%. Time-series analysis revealed that lateralisation of paw use was sequentially dependent. Muskoxen tended to use the same paw for one ensuring bout, but were also inclined tp switch sides over durations of 4 bouts. The lack of lateral bias, at least for this behaviour, contrasts with the general, emerging pattern for the Mammalia.