Pia Ley

Enhanced reactivity to visual stimuli in deaf individuals

PURPOSE Several studies have reported faster response time to visual stimuli in profoundly deaf individuals. This result is often linked to the processing of peripheral targets, and it is assumed to occur in relation to attention orienting. We evaluated whether enhanced reactivity to visual events in profoundly deaf individuals can be explained by faster orienting of visual attention alone. METHODS We examined 11 deaf individuals and 11 hearing controls, in a simple detection task and in a shape discrimination task. While simple detection can be performed under distributed attention, shape discrimination requires orienting of spatial attention to the target. The same visual targets served for both tasks, presented at central or peripheral locations and corrected for cortical magnification. RESULTS The simple detection task revealed faster RTs in deaf than hearing controls, regardless of target location. Moreover, while hearing controls paid a cost in responding to peripheral than central targets, deaf participants performed equally well regardless of target eccentricity. In the shape discrimination task deaf never outperformed hearing controls. CONCLUSIONS These findings reveal that enhanced reactivity to visual stimuli in the deaf cannot be explained only by faster orienting of visual attention and can emerge for central as well as peripheral targets. Moreover, the persisting advantage for peripheral locations in the deaf, observed here under distributed attention, suggests that this spatially-selective effect could result from reorganised sensory processing rather than different attentional gradients.

Sensitive periods for the functional specialization of the neural system for human face processing

Significance Sensitive periods in human functional brain development were tested in humans who had been blind from birth and whose sight was restored as long as 14 y later. In investigating this rare population, our data demonstrate a general principle of brain development: rather than being born with highly specialized neural systems (e.g., for specific object categories such as faces), the functional differentiation of neural circuits seems to depend on early (visual) experience involving a decrease in responsiveness to certain events during sensitive periods. The functional tuning of neural systems seems necessary to achieve high processing proficiency. The aim of the study was to identify possible sensitive phases in the development of the processing system for human faces. We tested the neural processing of faces in 11 humans who had been blind from birth and had undergone cataract surgery between 2 mo and 14 y of age. Pictures of faces and houses, scrambled versions of these pictures, and pictures of butterflies were presented while event-related potentials were recorded. Participants had to respond to the pictures of butterflies (targets) only. All participants, even those who had been blind from birth for several years, were able to categorize the pictures and to detect the targets. In healthy controls and in a group of visually impaired individuals with a history of developmental or incomplete congenital cataracts, the well-known enhancement of the N170 (negative peak around 170 ms) event-related potential to faces emerged, but a face-sensitive response was not observed in humans with a history of congenital dense cataracts. By contrast, this group showed a similar N170 response to all visual stimuli, which was indistinguishable from the N170 response to faces in the controls. The face-sensitive N170 response has been associated with the structural encoding of faces. Therefore, these data provide evidence for the hypothesis that the functional differentiation of category-specific neural representations in humans, presumably involving the elaboration of inhibitory circuits, is dependent on experience and linked to a sensitive period. Such functional specialization of neural systems seems necessary to archive high processing proficiency.

Partial recovery of visual-spatial remapping of touch after restoring vision in a congenitally blind man.

In an initial processing step, sensory events are encoded in modality specific representations in the brain but seem to be automatically remapped into a supra-modal, presumably visual-external frame of reference. To test whether there is a sensitive phase in the first years of life during which visual input is crucial for the acquisition of this remapping process, we tested a single case of a congenitally blind man whose sight was restored after the age of two years. HS performed a tactile temporal order judgment task (TOJ) which required judging the temporal order of two tactile stimuli, one presented to each index finger. In addition, a visual-tactile cross-modal congruency task was run, in which spatially congruent and spatially incongruent visual distractor stimuli were presented together with tactile stimuli. The tactile stimuli had to be localized. Both tasks were performed with an uncrossed and a crossed hand posture. Similar to congenitally blind individuals HS did not show a crossing effect in the tactile TOJ task suggesting an anatomical rather than visual-external coding of touch. In the visual-tactile task, however, external remapping of touch was observed though incomplete compared to sighted controls. These data support the hypothesis of a sensitive phase for the acquisition of an automatic use of visual-spatial representations for coding tactile input. Nonetheless, these representations seem to be acquired to some extent after the end of congenital blindness but seem to be recruited only in the context of visual stimuli and are used with a reduced efficiency.

Phenomenological differences between acute and chronic forms of major depression in inpatients

Background. Chronic forms of depression are highly prevalent especially in inpatient settings. Defined only by episode duration greater than 2 years, heterogeneous diagnoses like dysthymic disorder, double depression, major depression and recurrent major depression are included. Chronic depression is considered difficult to treat, although its distinguishing characteristics remain unclear. Aims. The purpose of the present study was empirically to approach proposed differences between acute and chronic forms of depression. Methods. 80 psychiatric inpatients positively screened for depression and diagnosed with the Composite International Diagnostic Interview (CIDI), completed a set of questionnaires regarding symptom severity (a simplified version of the Beck Depression Inventory), dysfunctional attitudes (Dysfunctional Attitudes Scale), ruminative response style (Response Styles Questionnaire, Why Ruminate Scale) and interpersonal problems (Inventory of Interpersonal Problems; IIP). Results. 30 patients were diagnosed with chronic forms of depression; 34 patients with acute depression. Patients did not differ regarding symptom severity, ruminative response styles, all but one subscales of the IIP or presence of comorbid post-traumatic stress disorder. However, chronic depression did show higher dysfunctional attitudes than acute depression, and reported higher rates of socially avoidant behavior. Conclusions. In line with previous findings, acute and chronic forms of depression differed in dysfunctional attitudes, which might actually reflect a distinguishing pattern of chronicity. Chronic depression patients also reported higher socially avoidant behavior, which might be crucial to focus in treatment. Surprisingly, other variables that are assumed to characterize chronic depression could not be confirmed as distinguishing features. Future research should take etiological aspects into account.

Kann man chronische Depression effektiv psychotherapeutisch behandeln

Chronische Depression gilt in der klinischen Praxis als besonders schwer behandelbar. Die Befundlage zu dieser Annahme ist jedoch unbefriedigend. Die wenigen existierenden Effektivitatsstudien zu verschiedenen Formen von Psychotherapie bei chronischen Depressionen (z. B. KVT, IPT, CBASP) zeigen tatsachlich, dass die Wirksamkeit eines rein psychotherapeutischen Vorgehens bei chronischen Depressionen begrenzt zu sein scheint; es gibt jedoch Hinweise auf additive Effekte im Rahmen einer Kombinationsbehandlung mit Psychopharmaka. Welchen spezifischen Nutzen neue oder modifizierte Behandlungsverfahren gegenuber klassischen Behandlungsverfahren haben, ist offen, da bislang keine Studien existieren, die diese Verfahren direkt mit klassischen Behandlungsansatzen vergleichen. Weiterhin offen bleibt, inwieweit die schlechten Behandlungsergebnisse tatsachlich der Chronizitat der depressiven Storung geschuldet sind, oder ob andere Faktoren, wie eine hohe Achse-II-Komorbiditat, den Ausschlag dafur geben.

The neural development of the biological motion processing system does not rely on early visual input

Naturally occurring sensory deprivation in humans provides a unique opportunity to identify sensitive phases for the development of neuro-cognitive functions. Patients who had experienced a transient period of congenital visual deprivation due to bilateral dense cataracts (congenital cataract, cc) have shown, after visual re-afferentation, deficits in a number of higher visual functions including global motion and face processing. By contrast, biological motion (BM) perception seemed to be spared. The present study investigated the neural correlates of BM processing in a sample of 12 congenital cataract-reversal individuals who had underwent visual restoration surgery at the age of a few months up to several years. The individual threshold for extracting BM from noise was assessed in a behavioral task while event-related potentials (ERPs) were recorded in response to point-light displays of a walking man and of a scrambled version of the same stimuli. The threshold of the cc group at detecting BM did not differ from that of a group of matched controls (mc). In both groups, the N1 was modulated by BM. These largely unimpaired neural responses to BM stimuli together with a lack of behavioral group differences suggest that, in contrast to the neural systems for faces the neural systems for BM processing specialize independent of early visual input.

Event‐related potential evidence for a dynamic (re‐) weighting of somatotopic and external coordinates of touch during visual–tactile interactions

The localization of touch in external space requires the remapping of somatotopically represented tactile information into an external frame of reference. Several recent studies have highlighted the role of posterior parietal areas for this remapping process, yet its temporal dynamics are poorly understood. The present study combined cross‐modal stimulation with electrophysiological recordings in humans to trace the time course of tactile spatial remapping during visual–tactile interactions. Adopting an uncrossed or crossed hand posture, participants made speeded elevation judgments about rare vibrotactile stimuli within a stream of frequent, task‐irrelevant vibrotactile events presented to the left or right hand. Simultaneous but spatially independent visual stimuli had to be ignored. An analysis of the recorded event‐related potentials to the task‐irrelevant vibrotactile stimuli revealed a somatotopic coding of tactile stimuli within the first 100 ms. Between 180 and 250 ms, neither an external nor a somatotopic representation dominated, suggesting that both coordinates were active in parallel. After 250 ms, tactile stimuli were coded in a somatotopic frame of reference. Our results indicate that cross‐modal interactions start before the termination of tactile spatial remapping, that is within the first 100 ms. Thereafter, tactile stimuli are represented simultaneously in both somatotopic and external spatial coordinates, which are dynamically (re‐)weighted as a function of processing stage.

Sight restoration after congenital blindness does not reinstate alpha oscillatory activity in humans

Functional brain development is characterized by sensitive periods during which experience must be available to allow for the full development of neural circuits and associated behavior. Yet, only few neural markers of sensitive period plasticity in humans are known. Here we employed electroencephalographic recordings in a unique sample of twelve humans who had been blind from birth and regained sight through cataract surgery between four months and 16 years of age. Two additional control groups were tested: a group of visually impaired individuals without a history of total congenital blindness and a group of typically sighted individuals. The EEG was recorded while participants performed a visual discrimination task involving intact and scrambled biological motion stimuli. Posterior alpha and theta oscillations were evaluated. The three groups showed indistinguishable behavioral performance and in all groups evoked theta activity varied with biological motion processing. By contrast, alpha oscillatory activity was significantly reduced only in individuals with a history of congenital cataracts. These data document on the one hand brain mechanisms of functional recovery (related to theta oscillations) and on the other hand, for the first time, a sensitive period for the development of alpha oscillatory activity in humans.

Dissociating Effects of Movement Preparation and Spatial Attention on Visual Processing: Evidence from Event-Related Potentials

The present study investigated whether effects of movement preparation and visual spatial attention on visual processing can be dissociated. Movement preparation and visual spatial attention were manipulated orthogonally in a dual-task design. Ten participants covertly prepared unimanual lateral arm movements to one hemifield, while attending to visual stimuli presented either in the same or in the hemifield opposite to the movement goal. Event-related potentials to task-irrelevant visual stimuli were analysed. Both joint and distinct modulations of visual ERPs by visual spatial attention and movement preparation were observed: The latencies of all analysed peaks (P1, N1, P2) were shorter for matching (in terms of direction of attention and movement) versus non-matching sensory-motor conditions. The P1 amplitude, as well, depended on the sensory-motor matching: The P1 was larger for non-matching compared to matching conditions. By contrast, the N1 amplitude showed additive effects of sensory attention and movement preparation: with attention and movement preparation directed towards the visual stimulus the N1 was largest, with both directed opposite to the stimulus the N1 was smallest. P2 amplitudes, instead, were only modulated by sensory attention. The present data show that movement preparation and sensory spatial attention are tightly linked and interrelated, showing joint modulations throughout stimulus processing. At the same time, however, our data argue against the idea of identity of the two systems. Instead, sensory spatial attention and movement preparation seem to be processed at least partially independently, though still exerting a combined influence on visual stimulus processing.

Dissociating sensory attention and motor preparation: An ERP study

Sensory and motor systems are closely linked as expressed in the Premotor Theory of Attention (PMTA, Rizzolatti et al., 1987). The PMTA predicts that sensory attention effects on stimulus processing are equivalent to an explicit or implicit motor preparation towards these stimuli. This view has been supported by findings suggesting a high overlap of neural systems involved in attention control and motor preparation (Corbetta et al., 1998). However, attempts to dissociate sensory attention and motor preparation effects, which, if possible, would argue against the PMTA, are still lacking. Eleven participants (8 female, mean age: 24 years (20–32 years)) performed a dual task: First they were verbally instructed to prepare a unimanual movement either towards the center, the left or the right side (motor attention). During the movement preparation phase a stream of visual stimuli was presented in the left and the right hemifield. Keeping central fixation participants had to detect rare color changes in one hemifield (left or right), while ignoring all other stimuli. After a variable interval (1–10 s) an auditory stimulus was presented that instructed the participants to execute the movement. This experimental paradigm allowed us to dissociate sensory and motor attention effects on visual stimulus processing. We analyzed the behavioral response to target stimuli and the visually ERPs to irrelevant visual stimuli at frontal, central and occipital cluster sites at three different time windows centered over the P1, the N1 and the N2. Both effects of sensory and motor attention as well as the interaction were analyzed.