Spatially Filtered Emotional Faces Dominate during Binocular Rivalry.

The present investigation explores the role of bottom-up and top-down factors in the recognition of emotional facial expressions during binocular rivalry. We manipulated spatial frequencies (SF) and emotive features and asked subjects to indicate whether the emotional or the neutral expression was dominant during binocular rivalry. Controlling the bottom-up saliency with a computational model, physically comparable happy and fearful faces were presented dichoptically with neutral faces. The results showed the dominance of emotional faces over neutral ones. In particular, happy faces were reported more frequently as the first dominant percept even in the presence of coarse information (at a low SF level: 2-6 cycle/degree). Following current theories of emotion processing, the results provide further support for the influence of positive compared to negative meaning on binocular rivalry and, for the first time, showed that individuals perceive the affective quality of happiness even in the absence of details in the visual display. Furthermore, our findings represent an advance in knowledge regarding the association between the high- and low-level mechanisms behind binocular rivalry.

Inhibition of return at foveal and extrafoveal locations: re-assessing the evidence.

Inhibition of return (IOR) has been described as a hallmark of externally controlled orienting of attention using extrafoveal cues and targets. This paper describes an IOR like inhibition of reaction time for the detection of targets at the fovea that cannot be explained by shift of covert attention. This foveal RT inhibition adds to the evidence that challenges the view of IOR-like phenomena as obligatory expressions of orienting and attentional control.

Semantic category effects modulate visual priming in neglect patients.

Previous studies indicate that extinguished stimuli can still be unconsciously processed, leading to implicit priming effects. Here we investigated whether these implicit effects might be modulated by the semantic nature of the stimuli. Five neglect patients and ten controls performed an identification task of items belonging to living and non-living categories. In the study phase photographs of animals and artifacts were presented either to the left visual field (LVF) or to the right visual field (RVF). In the identification phase, each stimulus was displayed centrally and was revealed in a sequence of frames where the item was represented by an increasingly less and less filtered image up to a complete version. The results showed that lateralized stimuli differentially affected controls' and neglect patients' memory retrieval. In controls memory traces from the study phase served as efficient primes, thereby reducing the amount of information necessary for the identification of both stimulus categories. Moreover, hemispheric differences emerged with an advantage of the RVF/left hemisphere for artifact items, while no difference was found for living things. Neglect patients showed a priming effect for artifact items presented either to the RVF/left hemisphere or LVF/right hemisphere, as well as for living items presented to the RVF/left hemisphere, but not for living items presented to the LVF/right hemisphere. The priming effect observed for extinguished artifacts is consistent with the evidence of the existence of a specific mechanism destined to analyze, in an automatic and implicit fashion, motor-relevant information of manipulable objects and tools, which are important for identification process. Results are discussed in relation to current models of organization of conceptual knowledge within the framework of different processes performed by the two hemispheres.

Sluggish engagement and disengagement of non-spatial attention in dyslexic children.

Although the dominant view posits that developmental dyslexia arises from a deficit in phonological processing and memory, efficient phonological decoding requires precise visual selection of graphemes. Therefore, visual engagement and disengagement of non-spatial attention were studied in 13 dyslexic children and 13 chronological age and intelligence quotient (IQ) matched normally reading children by measuring "attentional masking" (AM) and "attentional blink" (AB) effects. AM refers to an impaired identification of the first (T1) of two rapidly sequential targets (i.e., attentional engagement). In contrast, AB refers to an impaired identification of the second target in the sequence (T2; i.e., attentional disengagement). The results revealed a specific temporal deficit of AM as well as of AB in dyslexic children. Our results showed that the abnormality in AM and AB is rather widespread, since 77% and 54% of dyslexic children deviated at least 1 standard deviation (SD) from the mean of the controls, respectively, for the two deficits. We further showed that individual differences in non-spatial attention were specifically related to nonword reading ability. These results suggest that non-spatial attention deficits (possibly related to a parietal cortex dysfunction) may selectively impair the reading development via sub-lexical mechanisms.

To know what it is for, but not how it is: semantic dissociations in a case of visual agnosia.

We report the case of a woman who displayed impaired object recognition following a severe head injury. Her elementary visual functions were substantially preserved, allowing her a coherent percept. On the other hand, she was impaired in accessing stored knowledge from both visual and verbal input. In particular, she showed a dramatic dissociation between fully preserved access to functional knowledge, and severely impaired access to perceptual knowledge so that she could describe what objects are for, but not how they are. Our findings from this case suggest that different categories of object knowledge are represented independently in separate units within the semantic system.

Local (focussed) and global (distributed) visual processing in hemispatial neglect.

In the present study we set out to investigate deficits of focussed and distributed attention (and their interaction) in brain-damaged patients. To this purpose, four left brain damaged (LBD) patients without signs of hemispatial neglect and six right brain damaged (RBD) patients with variable signs of hemispatial neglect were tested by means of an experimental paradigm comprising two embedded tasks performed on the same visual array. The first task (i.e. counting the number of shapes, 1-4, briefly displayed) mainly involved distributed attention rather than focussed attention. The second task was a typical target detection task, which emphasized the detailed analysis of each element in the array, thus mainly tapping focussed attention. Results clearly showed that: (1) LBD patients are slightly impaired at directing focussed attention to the contralesional visual hemifield; (2) in comparison to LBD patients, RBD patients with mild neglect show an exaggerated difficulty in orienting focussed attention toward the contralesional side, while they are similarly unimpaired in the deployment of distributed attention, i.e. in global processing; (3) RBD patients with the most severe neglect suffer from a deficit of both local and global visual processing, i.e. of both focussed and distributed attention. Taken together, these observations indicate that focussed and distributed components of visual attentional processing may be differentially affected in left and right brain-damaged patients with and without neglect.

Poor readers but compelled to read: Stroop effects in developmental dyslexia.

We studied a group of 24 children with dyslexia in second to fifth primary school grades by using a discrete-trial computerized version of the Stroop Color-Word Test. Since the classic Stroop effect depends on the interference of reading with color naming, one would expect these children to show no interference or, at least, less interference than normal readers. Children with dyslexia showed, however, a Stroop effect larger than normal readers of the same age. This suggests that reading, although difficult and slow, is an inescapable step that precedes naming both in poor and in normal readers.

When supine is better than upright: evidence from postural effects in extinction patients.

There is no clear consensus on the specific effects of gravitational inputs on the manifestations of neglect and extinction. While some studies provided evidence that neglect patients improved their performance in supine position, other studies supported instead the notion that the manipulation of body posture has no effect on neglect and extinction. To investigate the effects of the postural manipulation of the entire body in space on visual extinction, a total of 24 right- and left-brain-damaged patients (with or without signs of visual extinction) and 8 healthy control subjects were tested in a visual detection task in two different gravitational conditions: upright and supine. Two dependent variables were considered: accuracy and speed of response. The results were clear-cut. Changing body posture had only a mild effect on the performance of healthy controls and non-extinction patients, but it clearly modulated the performance of extinction patients. In fact, extinction patients markedly improved their performance on contralesional stimuli in supine position in terms of both accuracy and speed of response. This suggests that the reduction of gravitational inputs obtained by placing patients in supine position results in a significant amelioration of visual extinction.

Gravitational influences on reference frames for mapping somatic stimuli in brain-damaged patients.

Previous studies have shown that the manipulation of body position in space can modulate the manifestations of visual neglect. Here, we investigated in right brain-damaged patients (RBD) the possible influence of gravitational inputs on the capability to detect tactile stimuli delivered to hands positioned in ipsilesional or contralesional space. RBD patients (with or without impairments in detecting contralesional stimuli under single and double stimulation conditions) and healthy control subjects were tested in a tactile detection task in which gravitational (upright vs. supine) and hand position (anatomical vs. crossed) variables were orthogonally varied. The postural manipulation of the entire body turned out to influence the degree of tactile detection. In particular, RBD patients with tactile deficits detected a significantly higher number of left-sided stimuli in the supine posture than in the upright posture. Moreover, crossing of hands improved the ability of RBD patients with tactile deficits in detecting stimuli delivered to their left contralesional hand. The beneficial effect of lying supine was independent of the spatial position of the hands, thus suggesting that the improvement of performance dependent upon entire-body posture and that dependent upon crossing hands may rely upon separate mechanisms.

Impairment of executive functions in a patient with a focal lesion in the anterior cingulate cortex. Evidence from neuropsychological assessment.

Patients with naturally occurring lesions involving the anterior cingulate cortex are rare and there thus exist very few reports of focal lesions in this area. We report a longitudinal study of a new case of selective anterior cingulate damage due to the presence of an angiocavernoma at the junction of the anterior third with the middle third of the right gyrus cinguli. Before surgery, the results of several, different tests suggested a significant impairment of executive functions, including deficits in planning, monitoring of ongoing behavior, and strategy shifting, as well as an exaggerated susceptibility to retroactive interference. Most of these symptoms disappeared completely or almost completely after the surgical removal of the angiocavernoma, although exaggerated susceptibility to interference was found to persist four months after surgery.

Temporary and permanent signs of interhemispheric disconnection after traumatic brain injury.

The corpus callosum is frequently damaged by closed head traumas, and the resulting deficits of interhemispheric communication may vary according to the specific position of the lesion within the corpus callosum. This paper describes a single case who suffered a severe traumatic brain injury resulting in a lesion of the posterior body of the corpus callosum. Among the classical symptoms of interhemispheric disconnection, left hand anomia, left upper limb ideomotor dyspraxia, left visual field dyslexia and dysnomia, and left ear suppression in a dichotic listening task were observed shortly after the injury but recovered completely or almost completely with the passage of time. The only symptom of interhemispheric disconnection which was found to persist more than 4 years after the injury was an abnormal prolongation of the crossed-uncrossed difference in a simple visuomotor reaction time task. This prolongation was comparable with that observed in subjects with complete callosal lesions or agenesis. The results suggest that the posterior body of the corpus callosum may be an obligatory interhemispheric communication channel for mediating fast visuo-motor responses. The transient nature of other symptoms of interhemispheric disconnection suggests a relatively wide dispersion of fibers with different functions through the callosal body, such that parts of them can survive a restricted lesion and allow functional recovery of hemispheric interactions. An assessment of the evolution in time of symptoms of interhemispheric disconnection following restricted callosal lesions may reveal fine and coarse features of the anatomo-functional topography of the corpus callosum.