Enhanced redundancy gain in schizophrenics: A correlate of callosal dysfunction?

The redundant target paradigm and its use as a blindsight-test: A meta-analytic study

The redundant target effect (RTE) is the well-known effect whereby a single target is detected faster when a second, redundant target is presented simultaneously. The RTE was shown in different experimental designs and applied in various clinical contexts. However, there are also studies showing non-effects or effects in the opposite direction. Our meta-analysis aims to investigate the replicability of the RTE. Herein, we focused on the clinical context within which the RTE has been applied most often and for which it gained particular prominence: The research on blindsight and other forms of residual vision in patients with damage to the neuronal visual system. The application of the RTE in clinical contexts assumes that whenever vision is present, an RTE will be found. Put differently, the RTE as a tool to uncover residual vision presumes that the RTE is a consistent feature of vision in the healthy population. We found a significant summary effect size of the RTE in healthy participants. The effect size depended on certain experimental features: task type, target configuration in the redundant condition, and how reaction times were computed in the single condition. A specific feature combination is typically used in blindsight research. Analyzing studies with this feature combination revealed a significant summary effect size in healthy participants predicting positive RTEs for future studies. A power-analysis revealed a required sample size of 14 participants to obtain an RTE with high reliability. However, the required sample size is rarely reached in blindsight research. Rather, blindsight research is mostly based on single-case studies. In summary, the RTE is a robust effect on group level but does not occur in every single individual. This means failure to obtain an RTE in a single patient should not be interpreted as evidence for the absence of residual vision in this patient.

Attention and masking in schizophrenia

BACKGROUND

Patients with schizophrenia are known to be impaired in masking tasks, but the mechanisms underlying their deficits are still elusive. Our study was intended to examine attentional effects, which have a known impact on masking in healthy volunteers but have only rarely been explored in relation to masking in patients.

METHODS

We compared focused versus divided attention in 18 control subjects and 18 patients using forward and backward masking tasks. In the conventional masking task, subjects had to locate one target among four possible locations. Presentation of one target allows attention to be focused, in contrast with the divided attention task in which two targets were presented either in the same hemifield or different hemifields.

RESULTS

Our results reproduce patients' deficits in forward and backward masking tasks but only when one target is presented. We show that control subjects benefit from focused attention, much more so than patients. Furthermore, patients' performance is identical to that of control subjects in backward masking when targets are presented across hemifields. This performance equalization was checked to ensure it was not due solely to the redundancy of signals (two vs. one). We achieved this by comparing performance when two targets were presented in the same vs. across hemifields, the latter yielding a greater redundancy gain.

CONCLUSIONS

From the results, it is unlikely that redundancy can account for the whole pattern of results, which suggest instead that attention deficits play a role in backward masking impairments in patients.

Perception of emotion and bilateral advantage in women with eating disorders, their healthy sisters, and nonrelated healthy controls

BACKGROUND

Eating disorders (EDs) are characterized not only by disordered eating, but also by other psychopathology. In this exploratory study, we examined the ability of women with different diagnoses of EDs, their unaffected sisters, and healthy unrelated controls to recognize their own and other's emotions. We also looked at interhemispheric integration of emotion recognition and its relationship with depression.

METHOD

Five groups of women participated: 1. anorexia nervosa restricting (AN-R) and 2. (AN-B/B) binge/purge, 3. bulimia nervosa binge/purge, (BN-B/P), 4. healthy sisters of women with ED, and 5. unrelated healthy controls. We used two questionnaires measuring alexithymia and depression, and two lateralized experimental tasks requiring recognition of facial emotion. Unilateral versus bilateral presentation allow the indexing of interhemispheric integration.

RESULTS

Alexithymia: All the ED groups were found to be more alexithymic and depressed on the self report scales compared to the two healthy groups. Depression completely mediated alexithymia in the AN-R group but not in the AN-B/P and BN-B/P patients. Sisters of ED women were more alexithymic than unrelated controls. Lateralized facial emotion recognition: ED women showed no deficits in recognizing basic emotions. However, the clinical groups did not show a bilateral advantage whereas the two healthy groups did so.

CONCLUSIONS

We present three conclusions: we show, for the first time, evidence for a deficit in hemispheric integration in EDs. This implies that EDs may be a disconnection syndrome; alexithymia characterizes women with EDs and members of their family; depression is manifested differently in AN-R, than in women who binge/purge.

ERP evidence of hemispheric independence in visual word recognition

This study examined the capability of the left hemisphere (LH) and the right hemisphere (RH) to perform a visual recognition task independently as formulated by the Direct Access Model (Fernandino, Iacoboni, & Zaidel, 2007). Healthy native Hebrew speakers were asked to categorize nouns and non-words (created from nouns by transposing two middle letters) into man-made and natural categories while their performance and ERPs were recorded. The stimuli were presented parafoveally to the right and left visual fields. As predicted by the Direct Access Model, ERP data showed that both the left hemisphere and right hemisphere were able to differentiate between words and non-words as early as 170 ms post-stimulus; these results were significant only for the contralaterally presented stimuli. The N1 component, which is considered to reflect orthographic processing, was larger in both hemispheres in response to the contralateral than the ipsilateral presented stimuli. This finding provides evidence for the RH capability to access higher level lexical information at the early stages of visual word recognition, thus lending weight to arguments for the relatively independent nature of this process.