Roberta Daini

Auditory sustained attention is a marker of unilateral spatial neglect

The relationships between performance on a non-spatially-lateralized measure of sustained attention and spatial bias on tests sensitive to unilateral neglect were considered in a group of 44 patients with right hemisphere lesions following stroke. As predicted from earlier studies showing a strong association between unilateral spatial neglect and sustained attention, performance on a brief and monotonous tone-counting measure formed a significant predictor of spatial bias across a variety of measures of unilateral visual neglect. This study provides further evidence for a very close link between two attentional systems hitherto regarded as being quite separate, namely a spatial attention system implicated in unilateral neglect and a sustained attention system. A close connection between these two systems was predicted by Posner, who argued that the right hemisphere-dominant sustained attention system provides a strong modulatory influence on the functioning of the lateralized posterior attention system.

Exploring the syndrome of spatial unilateral neglect through an illusion of length

Both a neuropsychological syndrome (unilateral spatial neglect) and a visual illusion of length (the Brentano version of the Müller-Lyer illusion) bring about a misjudgement of the subjective centre of a horizontal line, with a unilateral shift. In experiment 1 we investigated, in patients with left unilateral neglect, illusory effects of horizontal length, with the aim of exploring the functional and neural basis of horizontal space perception, and the role of visual processing in shaping the patients’ bisection performance. Fourteen right-brain-damaged patients with left spatial unilateral neglect, seven with and seven without left visual half-field deficits (assessed by confrontation, perimetry, and visual event-related potentials), entered this study. Two conditions of manual line bisection were assessed: setting the mid-point of a horizontal line, and of the shaft of the Brentano-Müller-Lyer illusion, with either a left- or a right-sided expansion. Both groups of patients set the subjective midpoint to the right of the objective centre of the line, consistent with the presence of left neglect. Patients with neglect and left hemianopia showed no illusory effects and a greater bisection error. The effects of the illusion, by contrast, were fully present in neglect patients without hemianopia, in both illusory conditions, adding to, or subtracting from, the rightward bisection bias. Anatomoclinical correlations revealed an association of damage to the occipital regions with the lack of illusory effects. Conversely, more anterior damage, sparing these regions, did not disrupt the illusion, revealing a dissociation between visual and spatial processing of extension. These findings suggest that processing of the Müller-Lyer illusion of length is likely to occur in the occipital cortex, at a retinotopic level of representation. In neglect patients with left homonymous hemianopia the visual deficit adds to the spatial bias, yielding a greater error in line bisection, but not in other visual exploratory tasks, such as cancellation, where the contribution of retinotopic frames is likely to be comparatively minor. Experiment 2 showed preserved illusory effects in patients with homonymous visual field defects without spatial unilateral neglect, suggesting that preserved spatial processing may compensate for unilateral visual field defects.

Processing of illusion of length in spatial hemineglect: a study of line bisection.

Bisection of horizontal lines and of the Brentano form of the Müller-Lyer illusion was investigated in six right brain-damaged patients with left spatial hemineglect, and in six control subjects. Patients bisected the lines to the right of the objective mid-point. Comparable illusory effects on line bisection were however found in both patients and control subjects. Relative to the baseline condition, in both groups the subjective midpoint was displaced towards the side expanded by the illusion, both leftwards and rightwards. By contrast, line length and spatial position of the stimulus had differential effects. In neglect patients, the rightward bisection error increased disproportionately with line length, and when the stimulus was located in the left, neglected, side of egocentric space. Control subjects showed no such effects. The suggestion is made that the visual, non-egocentric, processes underlying these illusory effects of length may be spared in patients with left spatial neglect. The possible neural basis of this dissociation is discussed.

Do People Have Insight into their Face Recognition Abilities

Diagnosis of developmental or congenital prosopagnosia (CP) involves self-report of everyday face recognition difficulties, which are corroborated with poor performance on behavioural tests. This approach requires accurate self-evaluation. We examine the extent to which typical adults have insight into their face recognition abilities across four experiments involving nearly 300 participants. The experiments used five tests of face recognition ability: two that tap into the ability to learn and recognize previously unfamiliar faces [the Cambridge Face Memory Test, CFMT; Duchaine, B., & Nakayama, K. (2006). The Cambridge Face Memory Test: Results for neurologically intact individuals and an investigation of its validity using inverted face stimuli and prosopagnosic participants. Neuropsychologia, 44(4), 576–585. doi:10.1016/j.neuropsychologia.2005.07.001; and a newly devised test based on the CFMT but where the study phases involve watching short movies rather than viewing static faces—the CFMT-Films] and three that tap face matching [Benton Facial Recognition Test, BFRT; Benton, A., Sivan, A., Hamsher, K., Varney, N., & Spreen, O. (1983). Contribution to neuropsychological assessment. New York: Oxford University Press; and two recently devised sequential face matching tests]. Self-reported ability was measured with the 15-item Kennerknecht et al. questionnaire [Kennerknecht, I., Ho, N. Y., & Wong, V. C. (2008). Prevalence of hereditary prosopagnosia (HPA) in Hong Kong Chinese population. American Journal of Medical Genetics Part A, 146A(22), 2863–2870. doi:10.1002/ajmg.a.32552]; two single-item questions assessing face recognition ability; and a new 77-item meta-cognition questionnaire. Overall, we find that adults with typical face recognition abilities have only modest insight into their ability to recognize faces on behavioural tests. In a fifth experiment, we assess self-reported face recognition ability in people with CP and find that some people who expect to perform poorly on behavioural tests of face recognition do indeed perform poorly. However, it is not yet clear whether individuals within this group of poor performers have greater levels of insight (i.e., into their degree of impairment) than those with more typical levels of performance.

Two different mechanisms for omission and substitution errors in neglect dyslexia

Neglect dyslexia is a reading disorder often associated with right-sided brain lesions. In reading single words, errors are mostly substitutions or omissions of letters that occupy the left-sided positions. Typically, these errors have been thought to depend on a single mechanism. Conversely, we propose that they are due to different mechanisms. In particular, a visuo-spatial mechanism is responsible for omissions and a perceptual integration process for substitution errors. We measured the performance of six patients with both neglect and neglect dyslexia, analyzing their reading errors as a function of letter spacing. According to our conjecture, letter spacing should increase omissions by moving part of the string further in the unattended space, while it should reduce substitutions by restoring the integration processes. Furthermore, we predict that letter spacing should be more effective with pseudowords compared to words, in that in this latter case lexical effects are supposed to influence attentional and perceptual processes. Accordingly, we found that for pseudowords only the two types of errors are differently affected by this manipulation and only omissions correlate with the severity of the disorder in visuo-spatial tasks.

A stimulus-centered reading disorder for words and numbers: Is it neglect dyslexia?

A single case, RCG, showing a unilateral reading disorder without unilateral spatial neglect was studied. The disorder was characterized by substitutions of the initial (left) letters of words, nonwords and Arabic numbers, independently of egocentered spatial coordinates. MRI showed a bilateral lesion with the involvement of the splenium. Although, within the framework of the visual word recognition model proposed by Caramazza and Hillis (1990), RCG disorder could be defined as a stimulus-centered neglect dyslexia, we discuss the hypothesis of a dissociation in neural correlates and mechanisms between the syndrome of unilateral spatial neglect and such a unilateral reading disorder.

Neglect dyslexia: a matter of "good looking".

Brain-damaged patients with right-sided unilateral spatial neglect (USN) often make left-sided errors in reading single words or pseudowords (neglect dyslexia, ND). We propose that both left neglect and low fixation accuracy account for reading errors in neglect dyslexia. Eye movements were recorded in USN patients with (ND+) and without (ND-) neglect dyslexia and in a matched control group of right brain-damaged patients without neglect (USN-). Unlike ND- and controls, ND+ patients showed left lateralized omission errors and a distorted eye movement pattern in both a reading aloud task and a non-verbal saccadic task. During reading, the total number of fixations was larger in these patients independent of visual hemispace, and most fixations were inaccurate. Similarly, in the saccadic task only ND+ patients were unable to reach the moving dot. A third experiment addressed the nature of the left lateralization in reading error distribution by simulating neglect dyslexia in ND- patients. ND- and USN- patients had to perform a speeded reading-at-threshold task that did not allow for eye movements. When stimulus exploration was prevented, ND- patients, but not controls, produced a pattern of errors similar to that of ND+ with unlimited exposure time (e.g., left-sided errors). We conclude that neglect dyslexia reading errors may arise in USN patients as a consequence of an additional and independent deficit unrelated to the orthographic material. In particular, the presence of an altered oculo-motor pattern, preventing the automatic execution of the fine saccadic eye movements involved in reading, uncovers, in USN patients, the attentional bias also in reading single centrally presented words.

Aftereffect induced by prisms of different power in the rehabilitation of neglect: A multiple single case report

OBJECTIVES Prism Adaptation (PA) is a technique used in the rehabilitation of unilateral spatial neglect. Several researchers have reported positive results on a number of tasks, but negative outcomes have also been reported. These conflicting results could be due to the use of prisms of different power. The aim of this study was to investigate the amplitude and duration of the aftereffect induced by prisms of different power by different measures in a series of single cases of neglect. METHODS Five neglect patients and ten control subjects participated in the study. Prism adaptation was evaluated with Subjective Straight Ahead (SSA), Open-Loop Pointing (OLP) and Line Bisection (LB) tasks, immediately before prism adaptation, immediately after, and 10/60 minutes after prism adaptation. The procedure was repeated with prisms of 5, 10 and 20 prismatic diopters (Δ). RESULTS The OLP task provided the most sensitive measures for the size of the aftereffect. The 20Δ prism proved to be most effective in inducing an immediate aftereffect, while the aftereffect of the 5Δ prism seemed to last longer. CONCLUSION We showed that the prism power and the task used for assessing PA effect are relevant variables to be consider in clinical practice of neglect rehabilitation.

Dissociation in Optokinetic Stimulation Sensitivity between Omission and Substitution Reading Errors in Neglect Dyslexia

Although omission and substitution errors in neglect dyslexia (ND) patients have always been considered as different manifestations of the same acquired reading disorder, recently, we proposed a new dual mechanism model. While omissions are related to the exploratory disorder which characterizes unilateral spatial neglect (USN), substitutions are due to a perceptual integration mechanism. A consequence of this hypothesis is that specific training for omission-type ND patients would aim at restoring the oculo-motor scanning and should not improve reading in substitution-type ND. With this aim we administered an optokinetic stimulation (OKS) to two brain-damaged patients with both USN and ND, MA and EP, who showed ND mainly characterized by omissions and substitutions, respectively. MA also showed an impairment in oculo-motor behavior with a non-reading task, while EP did not. The two patients presented a dissociation with respect to their sensitivity to OKS, so that, as expected, MA was positively affected, while EP was not. Our results confirm a dissociation between the two mechanisms underlying omission and substitution reading errors in ND patients. Moreover, they suggest that such a dissociation could possibly be extended to the effectiveness of rehabilitative procedures, and that patients who mainly omit contralesional-sided letters would benefit from OKS.

Visual orientation illusions: Global mechanisms involved in hierarchical effects and frames of reference

Five experiments were conducted in order to determine which of two hypotheses, initially proposed by Rock (1990), accounts for interactions between oriented elements in a visual scene. We also explored the suggestion that two hypothetical processes—namely,frame of referenceand hierarchical organization— describe phenomena arising from distinct mechanisms (Spinelli, Antonucci, Daini, Martelli, & Zoccolotti, 1999). Double inducing stimulus versions of one-dimensional and two-dimensional tilt illusions, the rod-and-frame illusion, and combinations of these were used. Our data suggest that both hypotheses can predict orientation interactions in conditions in which only one mechanism—namely, the global visual mechanism of symmetry axes extraction (Wenderoth & Beh, 1977)—is activated. Which hypothesis is appropriate to predict the perceived orientation depends on some physical features of the objects.