Cerebral dominance and lateral differences in perception and memory

The present investigation was designed to replicate a previous finding that tachistoscopically presented complex forms of low verbal association value would be more accurately recognized when presented to the left visual field than to the right, thus implying dominance of the right hemisphere for the perception of this type of stimulus material. The successful replication of this finding was important because of previous unsuccessful attempts to show such an effect. This finding, in conjunction with the well established right visual field (i.e. left hemisphere) superiority for the perception of verbal material, strongly supports the hypothesis that asymmetry in human perceptual performance reflects hemispheric asymmetry of function rather than peripheral factors.The second question investigated concerned the role of memory in producing perceptual asymmetry. Complex figures were presented for 15–25 msec in either the left or right visual field; after a delay of 0–20 sec, the subject was required to indicate whether or not a form presented in central vision was the target form. The results indicate that the observed left visual field superiority for these complex forms appears to arise from hemispheric differences in memory rather than from purely perceptual processes.     

Cross-modal asymmetries in perception related to asymmetry in cerebral function

Cross-modal correlations between left-right asymmetry on the Dichotic Listening (D-L) test and a visual half-field ((VHF) test were obtained for 30 right-handed subjects with no family history of left-handedness, 30 right handed subjects with a positive family history of left-handedness and 30 left-handed subjects. Both groups of right-handed subjects demonstrated significant cross-modal correlations between the D-L (auditory) asymmetry and the VHF (visual) asymmetry. The left-handed subjects displayed no correlation between D-L and VHF asymmetries. This suggests a dissociation between auditory and visual laterality in left-handers. Differences between this finding and two previous studies which found no cross-modal asymmetry for right-or-left-handers are discussed. The visual half-field test utilized in this experiment controlled fixation by presenting digits sequentially at fixation, while simultaneously presenting other digits to either the right or left VHF. This procedure minimizes the effect of directional scanning on VHF asymmetry. The reliability of the D-L and VHF asymmetries was also computed. The D-L asymmetry proved to be highly reliable (r = 0.86), while the VHF asymmetry was somewhat less reliable (r = 0.46). The asymmetry on both tests was attributed to asymmetry of cerebral function.     

Dichotic listening asymmetries and psychotic symptoms in schizophrenia: a preliminary report

Schizophrenic subjects were compared with both psychiatric control and normal control groups on two verbal measures of functional hemispheric asymmetry on a dichotic listening task. One measure of language perception showed little variation in ear differences across groups. However, the task that contained both attentional and language-processing components showed variations in asymmetry according to symptomatology. Subjects with high scores on scales of hallucinations and delusions showed a pattern of ear differences that was not found in those with low scores on these symptom dimensions. The results may reflect cognitive factors in a dysfunctional information-processing system and, in particular, attentional disturbance rather than anomalies in the lateralization of language.     

Asymmetry of Recall in Depression

Abstract

We compared the verbal (auditory/semantic) and nonverbal (visual/configurational) recall of carefully defined depressed patients with a demographically matched control group of normal volunteers. Whereas controls were split as to whether their nonverbal recall exceeded or was inferior to their verbal recall, 89% of depressed patients demonstrated an asymmetry characterized by poorer nonverbal than verbal recall. Depressive subgroups (determined by clinical and psychoendocrine criteria) differed from controls, but not from each other, in demonstrating this asymmetry of recall. In contrast, depressed patients did not individually demonstrate an asymmetry between verbal and nonverbal recognition that differed from controls.     

Reduced visual contrast suppression during major depressive episodes

BackgroundPrevious studies have suggested that processing of visual contrast information could be altered in major depressive disorder. To clarify the changes at different levels of the visual hierarchy, we behaviourally measured contrast perception in 2 centre-surround conditions, assessing retinal and cortical processing.MethodsAs part of a prospective cohort study, our sample consisted of controls (n = 29; 21 female) and patients with unipolar depression, bipolar disorder and borderline personality disorder who had baseline major depressive episodes (n = 111; 74 female). In a brightness induction test that assessed retinal processing, participants compared the perceived luminance of uniform patches (presented on a computer screen) as the luminance of the backgrounds was varied. In a contrast suppression test that assessed cortical processing, participants compared the perceived contrast of gratings, which were presented with collinearly or orthogonally oriented backgrounds.ResultsBrightness induction was similar for patients with major depressive episodes and controls (p = 0.60, d = 0.115, Bayes factor = 3.9), but contrast suppression was significantly lower for patients than for controls (p < 0.006, d = 0.663, Bayes factor = 35.2). We observed no statistically significant associations between contrast suppression and age, sex, or medication or diagnostic subgroup. At follow-up (n = 74), we observed some normalization of contrast perception.LimitationsWe assessed contrast perception using behavioural tests instead of electrophysiology.ConclusionThe reduced contrast suppression we observed may have been caused by decreased retinal feedforward or cortical feedback signals. Because we observed intact brightness induction, our results suggest normal retinal but altered cortical processing of visual contrast during a major depressive episode. This alteration is likely to be present in multiple types of depression and to partially normalize upon remission.     

Dichotic listening in schizophrenic patients: effects of previous vs. ongoing auditory hallucinations

Auditory hallucinations (AH) in schizophrenia have been found to be related to both functional and structural brain abnormalities of left temporal lobe language areas. We do not know if these rain abnormalities are state or trait markers for AH. This study tested these alternatives by contrasting schizophrenic patients with ongoing AH and with a previous history of AH. A heterogeneous group of 26 schizophrenic patients was compared with a healthy control group matched for education and age. We used a verbal dichotic listening (DL) test with consonant-vowel syllables to study hemispheric asymmetry and the functional integrity of the left temporal lobe language areas. All subjects were tested during a divided and two focused attention conditions. Our data suggest that abnormal DL asymmetry for language stimuli is a state marker for AH, seen during the perception of AH. In contrast, problems of modulating DL performance by means of attentional control are a trait marker, seen both in patients with ongoing AH and only a history of AH.     

Asymmetry of recall in depression.

We compared the verbal (auditory/semantic) and nonverbal (visual/configurational) recall of carefully defined depressed patients with a demographically matched control group of normal volunteers. Whereas controls were split as to whether their nonverbal recall exceeded or was inferior to their verbal recall, 89% of depressed patients demonstrated an asymmetry characterized by poorer nonverbal than verbal recall. Depressive subgroups (determined by clinical and psychoendocrine criteria) differed from controls, but not from each other, in demonstrating this asymmetry of recall. In contrast, depressed patients did not individually demonstrate an asymmetry between verbal and nonverbal recognition that differed from controls.     

Cognitive impairments in patients with congenital nonprogressive cerebellar ataxia.

OBJECTIVE: To report neuropsychologic functions and developmental problems of patients with congenital nonprogressive cerebellar ataxia. BACKGROUND: Growing interest in cerebellar function has prompted closer attention to cognitive impairments in patients with cerebellar damage. METHODS: The authors studied 11 patients with nonprogressive congenital ataxia (NPCA) with Wechsler's intelligence testing, with additional tests of attention, memory, language, visual perception, and frontal functions. RESULTS: Seven of the 11 patients had an IQ of 60 to 92, with marked nonverbal deficits and subnormal to normal verbal performance (group A). Four patients had an IQ of 30 to 49 without pronounced profile asymmetry (group B). Four of the 7 group A patients had decreased alertness and sustained attention, but all had normal selective attention. Tests of frontal functions and memory yielded higher verbal scores than nonverbal scores. There was no deficit on the Aachener Naming Test (similar to the Boston Naming Test), because there were marked difficulties in the majority with visuoconstructive tasks and visual perception. Group B was significantly abnormal in almost all subtests, having a less prominent but similar profile. CONCLUSION: Patients with NPCA have significant cognitive deficits with an asymmetric profile and better verbal than nonverbal performance. Effects on nonverbal performance of longstanding deficits in visuospatial input during learning, the influence of impaired procedural learning, and asymmetric plasticity of the cerebral hemispheres may contribute to this uneven neuropsychological profile.     

From Receptive to Perceptive Fields: Size-Dependent Asymmetries in Both Negative Afterimages and Subcortical On and Off Post-Stimulus Responses

Negative afterimages are perceptual phenomena that occur after physical stimuli disappear from sight. Their origin is linked to transient post-stimulus responses of visual neurons. The receptive fields (RFs) of these subcortical ON- and OFF-center neurons exhibit antagonistic interactions between central and surrounding visual space, resulting in selectivity for stimulus polarity and size. These two features are closely intertwined, yet their relationship to negative afterimage perception remains unknown. Here we tested whether size differentially affects the perception of bright and dark negative afterimages in humans of both sexes, and how this correlates with neural mechanisms in subcortical ON and OFF cells. Psychophysically, we found a size-dependent asymmetry whereby dark disks produce stronger and longer-lasting negative afterimages than bright disks of equal contrast at sizes >0.8°. Neurophysiological recordings from retinal and relay cells in female cat dorsal lateral geniculate nucleus showed that subcortical ON cells exhibited stronger sustained post-stimulus responses to dark disks, than OFF cells to bright disks, at sizes >1°. These sizes agree with the emergence of center-surround antagonism, revealing stronger suppression to opposite-polarity stimuli for OFF versus ON cells, particularly in dorsal lateral geniculate nucleus. Using a network-based retino-geniculate model, we confirmed stronger antagonism and temporal transience for OFF-cell post-stimulus rebound responses. A V1 population model demonstrated that both strength and duration asymmetries can be propagated to downstream cortical areas. Our results demonstrate how size-dependent antagonism impacts both the neuronal post-stimulus response and the resulting afterimage percepts, thereby supporting the idea of perceptual RFs reflecting the underlying neuronal RF organization of single cells.SIGNIFICANCE STATEMENT Visual illusions occur when sensory inputs and perceptual outcomes do not match, and provide a valuable tool to understand transformations from neural to perceptual responses. A classic example are negative afterimages that remain visible after a stimulus is removed from view. Such perceptions are linked to responses in early visual neurons, yet the details remain poorly understood. Combining human psychophysics, neurophysiological recordings in cats and retino-thalamo-cortical computational modeling, our study reveals how stimulus size and the receptive-field structure of subcortical ON and OFF cells contributes to the parallel asymmetries between neural and perceptual responses to bright versus dark afterimages. Thus, this work provides a deeper link from the underlying neural mechanisms to the resultant perceptual outcomes.     

Persisting asymmetries of vision after right side lesions

Visual neglect and extinction are well-known effects of lesions in the right hemisphere. This study shows that even with minor or no clinical signs of these deficits, and in the stable phase of recovery, asymmetric visual perception is common after right side lesions. Whole, partial and colour report experiments were used to estimate psychophysical parameters related to visual capacity and attentional weighting in 26 patients with stroke in the right side of the brain. The results were analyzed using Bundesen's Theory of Visual Attention (TVA [Bundesen, C. (1990). A theory of visual attention. Psychological Review, 97, 523-547]) including bootstrap estimation of the measurement error related to each test result [Habekost, T., & Bundesen, C. (2003). Patient assessment based on a theory of visual attention (TVA): Subtle deficits after a right frontal-subcortical lesion. Neuropsychologia, 41, 1171-1188]. Lesions were examined by MR scanning and analyzed statistically. Two main types of deficit were found. The first type was related to perception of unilateral displays, where most patients showed left side reductions of visual processing speed. This visual asymmetry correlated with injury to the putamen and surrounding white matter. The second deficit type occurred with bilateral displays, which increased the visual asymmetry (extinction effect) for most patients with large cortico-subcortical lesions, but rarely for patients with focal lesions. However, in a single case with pulvinar damage, visual asymmetry occurred selectively with bilateral stimulation. Overall, the study provided an overview of the cognitive structure and lesion anatomy of subtle visual asymmetries after right side stroke.     

Assessing effects of fixation demands on perception of lateralized words: A visual window technique for studying hemispheric asymmetry

A major concern when using lateralized words to study hemispheric asymmetry is that the retinal eccentricity of targets is matched across visual hemifields. The standard technique is to fixate a point fixed at the centre of the visual field. However, the demands of this fixation task are substantial and so may confound performance with lateralized targets. To investigate this possibility, words were presented unilaterally in each visual hemifield and retinal eccentricity was controlled using (a) a fixed central point or (b) a window technique that permitted small shifts in fixation while maintaining accurate retinal eccentricity by using automatic adjustments to target location. Fixation errors and time to fixate indicated that the demands of the standard technique were considerable and far greater than those of the window technique. Nevertheless, both techniques produced the same pattern of visual field effects, indicating that the demands of fixating a fixed central point do not confound performance with lateralized words. However, the window technique was more efficient and easier for participants to use and so offers a new improved methodology for studying hemispheric asymmetry.     

Compromised verbal episodic memory with intact visual and procedural memory during pregnancy

This study investigated episodic and procedural memory performance in early and late pregnancy. Twenty-six women in the third trimester of pregnancy, 20 women in the first trimester of pregnancy, and 24 nonpregnant controls were administered a battery of verbal and visual episodic memory tasks and two procedural memory tasks. Results indicated that compared to controls, both pregnant groups had reduced scores on immediate and delayed verbal episodic memory tasks, but were unimpaired on visual and procedural memory tasks. Verbal memory differences could not be accounted for by mood state or attention; however, progesterone level accounted for a small amount of the variation. Although memory differences were minor, the perception of memory problems may have implications for everyday living for pregnant women.     

Hemispheric asymmetry and visuo-olfactory integration in perceiving subthreshold (micro) fearful expressions

Multisensory integration is ubiquitous, facilitating perception beyond the limit of individual senses. This mechanism is especially salient when individual sensory input is weak (i.e., the principle of inverse effectiveness), fusing subthreshold cues into tangible percepts. Nevertheless, it is unclear how this rule applies to threat perception, synthesizing elusive, discrete traces of a threat into a discernible danger signal. In light of hemispheric asymmetry in threat processing, we combined parafoveal stimulus presentation and the contralateral P1 visual event-related potential to investigate how aversive olfactory inputs enhance visual perception of highly degraded, subthreshold fearful expressions. The dominant right hemisphere exhibited early visual discrimination between subtle fear and neutral expressions, independently of accompanying odors. In the left hemisphere, differential visual processing occurred only at the convergence of negative odors and minute facial fear, highlighting the success and necessity of visuo-olfactory threat integration in this disadvantaged hemisphere. Reaction time data from a subsequent dot-detection task complemented these neural findings, revealing odor-dependent and hemisphere-specific modulation of spatial attention to facial expressions. Our evidence thus indicates cross-modal threat integration in basic visual perception in humans that captures minimal threat information, especially in the blind right hemifield. Critically, this interaction between multisensory synergy and hemispheric asymmetry in threat perception may underlie the multifaceted fear experiences of everyday life.     

Shadows of artistry: cortical synchrony during perception and imagery of visual art

Functional and topographical differences between two groups, artists and non-artists, during the performances of visual perception and imagery of paintings were presented by means of EEG phase synchrony analysis. In artists as compared with non-artists, significantly higher phase synchrony was found in the high frequency beta and gamma bands during the perception of the paintings; in the low frequency bands (primarily delta), phase synchrony was mostly enhanced during imagery. Strong decreases in phase synchrony of alpha were found primarily in artists for both tasks. The right hemisphere was found to present higher synchrony than the left in artists, whereas hemispheric asymmetry was less significant in non-artists. In the artists, enhanced synchrony in the high frequency band is most likely due to their enhanced binding capabilities of numerous visual attributes, and enhanced synchrony in the low frequency band seems to be due to the higher involvement of long-term visual memory mostly in imagery. Thus, the analysis of phase synchrony from EEG signals yields new information about the dynamical co-operation between neuronal assemblies during the cognition of visual art.     

Preoperative FDG-PET temporal lobe hypometabolism and verbal memory after temporal lobectomy

OBJECTIVE: To examine the relationship of preoperative fluorodeoxyglucose (FDG)-PET asymmetry in temporal lobe metabolism and memory outcome after anterior temporal lobectomy (ATL). METHODS: In a university-based epilepsy surgery center, 60 ATL patients (27 left, 33 right) were divided into two groups: no/mild (n = 21) or moderate/ severe (n = 39) asymmetry in temporal lobe hypometabolism as determined by FDG-PET. All patients were nonretarded, at least 18 years of age, left-hemisphere speech dominant, without MRI abnormalities other than hippocampal atrophy, and with unilateral temporal lobe origin of intractable complex partial seizures. Neuropsychological measures of intelligence and verbal and visual memory function were assessed preoperatively and 6 months postoperatively. RESULTS: Left ATL patients with no/mild asymmetry in FDG-PET temporal lobe metabolism exhibited significantly greater verbal memory decline compared with left ATL patients with moderate/severe hypometabolism. There was no significant relationship between PET asymmetry and pre- to postsurgical IQ change. No significant relationship was observed between extent of PET hypometabolism and memory outcome for right ATL patients. CONCLUSIONS: FDG-PET asymmetry can be added to the preoperative clinical markers that appear useful in predicting verbal memory decline after left ATL.     

Auditory and visual interactions between the superior and inferior colliculi in the ferret

The integration of visual and auditory spatial information is important for building an accurate perception of the external world, but the fundamental mechanisms governing such audiovisual interaction have only partially been resolved. The earliest interface between auditory and visual processing pathways is in the midbrain, where the superior (SC) and inferior colliculi (IC) are reciprocally connected in an audiovisual loop. Here, we investigate the mechanisms of audiovisual interaction in the midbrain by recording neural signals from the SC and IC simultaneously in anesthetized ferrets. Visual stimuli reliably produced band‐limited phase locking of IC local field potentials (LFPs) in two distinct frequency bands: 6–10 and 15–30 Hz. These visual LFP responses co‐localized with robust auditory responses that were characteristic of the IC. Imaginary coherence analysis confirmed that visual responses in the IC were not volume‐conducted signals from the neighboring SC. Visual responses in the IC occurred later than retinally driven superficial SC layers and earlier than deep SC layers that receive indirect visual inputs, suggesting that retinal inputs do not drive visually evoked responses in the IC. In addition, SC and IC recording sites with overlapping visual spatial receptive fields displayed stronger functional connectivity than sites with separate receptive fields, indicating that visual spatial maps are aligned across both midbrain structures. Reciprocal coupling between the IC and SC therefore probably serves the dynamic integration of visual and auditory representations of space.     

Relationship of affect recognition with psychopathology and cognitive performance in schizophrenia.

The purpose of the present study was to explore the relationship between emotion perception and both psychopathology and cognitive functioning in a group of Greek patients with schizophrenia. Thirty-five patients with schizophrenia were assessed with computerized tests of emotion perception, using visual faces (Kinney's Affect Matching Test, KAMT), prosody (Affective Prosody Test, APT), and visual everyday scenarios (Fantie's Cartoon Test, FCT), as well as a facial recognition test (Kinney's Identity Matching Test, KIMT). The patients were also evaluated with the symptoms dimensions derived from the PANSS (positive, negative, cognitive, depression, and excitement) and a battery of neuropsychological tests measuring executive functions, attention, working memory, verbal and visual memory, visuospatial ability, and visual scanning/psychomotor speed. The three emotion perception and face recognition tests correlated significantly with each other. The KAMT was significantly related to the cognitive symptoms dimension of the PANSS and executive functions. The FCT was significantly related to level of education and attention. Finally, the APT was significantly related to the cognitive symptoms dimension, executive functions, and attention. Our findings regarding the significant relationships of affect perception, both facial and vocal, as well as in everyday scenarios, with several cognitive abilities support the notion that deficits in decoding affective information in schizophrenia could be attributed to impairment in more basic neurocognitive domains.     

Dual functional hemispheric asymmetry in visual perception: Effects of ocular dominance and postexposural processes

The authors investigated laterality differences in visual perception by assessing the effects of the directional post-exposure scanning movements associated with reading habits, the visual half-field (VHF) in which stimuli were presented, and eye dominance on an immediate recall task. Forty Chinese bilingual subjects (20 right-eye dominant and 20 left-eye dominant) were tested for their recall of forms, Chinese words and English words. The stimuli were projected tachistoscopically in the left and/or right VHFs under conditions of simulataneous and successive presentation. The results demonstrated a right field superiority for verbal stimuli under both conditions and a left field superiority for nonverbal stimuli when presented successively. Right-eyed subjects were better in processing verbal materials and left-eyed subjects were better in the perception and recall of nonverbal materials. The study supported the validity of the psychophysiological model of asymmetrical cerebral functioning and demonstrated the importance of reading habits and eye dominance. The findings were interpreted as preliminary support for Piaget's postulated relationship between perceptual and organic development.     

Neural impact of the semantic content of visual mental images and visual percepts

The existence of hemispheric lateralization of visual mental imagery remains controversial. In light of the literature, we used fMRI to test whether processing of mental images of object drawings preferentially engages the left hemisphere to compared non-object drawings. An equivalent comparison was also made while participants actually perceived object and non-object drawings. Although these two conditions engaged both hemispheres, activation was significantly stronger in the left occipito-temporo-frontal network during mental inspection of object than of non-object drawings. This network was also activated when perception of object drawings was compared to that of non-object drawings. An interaction was nonetheless observed: this effect was stronger during imagery than during perception in the left inferior frontal and the left inferior temporal gyrus. Although the tasks subjects performed did not explicitly require semantic analysis, activation of this network probably reflected, at least in part, a semantic and possibly a verbal retrieval component when object drawings were processed. Mental imagery tasks elicited activation of early visual cortex at a lower level than perception tasks. In the context of the imagery debate, these findings indicate that, as previously suggested, figurative imagery could involve primary visual cortex and adjacent areas.     

Visual information processing in the left and right hemispheres

The effect of verbal vs nonverbal center fixation stimuli on visual half-field (VHF) asymmetry was investigated using both verbal and nonverbal VHF stimuli. Twenty adult subjects were administered word, face, and random shape VHF stimuli under both unilateral and bilateral viewing conditions.The results showed that VHF asymmetry was determined primarily by type of VHF stimuli under all viewing conditions. Words were recognized more often from the right VHF, faces were recognized more often from the left VHF, and random shapes showed no significant VHF difference. The results indicate that VHF asymmetry reflects differences in information processing capacity between the left and right hemispheres.