Search

Scientific research involves going beyond the well-trodden and well-tested ideas and theories that form the core of scientific knowledge. During the time scientists are working things out, some results will be right, and others will be wrong. Over time, the right results will emerge. Lisa Randall (Frank B. Baird, Jr. Professor of Science, Physics Department, Harvard University) We are grateful to all the commentators for the important and thoughtful comments raised in response to the Geskin and Behrmann (G & B) literature survey. The issues raised in the introduction to this Special Issue and in these commentaries not only address and challenge aspects of the G & B literature review, but contribute perspectives and extensions that go well beyond the scope of the review. As is evident from G & B and from the 13 commentaries, many aspects of congenital prosopagnosia (CP) remain controversial. Adopting the language of the quote above, the intention of the G & B survey, along with the commentaries and this response, is to establish a collaborative process from which the right results (and right theory) will emerge in time. We are grateful to the editor of this Special Issue, Dr. Brad Mahon, for his support and for facilitating this collaborative exchange in Cognitive Neuropsychology.

The deficit in face recognition in individuals with prosopagnosia has often been attributed to an underlying impairment in holistic processing. Exactly what constitutes holistic processing has remained controversial, however. Here, we compare how configural information and featural information interact during face processing in a group of individuals with congenital prosopagnosia (CP) and matched controls. We adopted Amishav and Kimchi's version of Garner's speeded classification task, in which observers classify upright faces based on configural (intereyes and nose-mouth spacing) or featural (shape of eyes, nose, and mouth) information while the other dimension remains constant or varied randomly. We replicated the finding that normal observers evince symmetric Garner interference--failure to selectively attend to features without being influenced by irrelevant variation in configuration, and vice versa--indicating that featural and configural information are integral in normal face processing. In contrast, the CPs showed no Garner interference: They were able to attend to configural information without interference from irrelevant variation in featural information, and they were able to attend to featural information without interference from irrelevant variation in configural information. The absence of Garner interference in CP provides strong evidence that featural information and configural information are perceptually separable in CP's face processing. These findings indicate that CPs do not perceive faces holistically; rather, they process featural and configural information independently.

Visual processing and naming of individual letters and short words were investigated in four patients with pure alexia. To test processing at different levels, the same stimuli were studied across a naming task and a visual perception task. The normal word superiority effect was eliminated in both tasks for all patients, and this pattern was more pronounced in the more severely affected patients. The relationship between performance with single letters and words was, however, not straightforward: One patient performed within the normal range on the letter perception task, while being severely impaired in letter naming and word processing, and performance with letters and words was dissociated in all four patients, with word reading being more severely impaired than letter recognition. This suggests that the word reading deficit in pure alexia may not be reduced to an impairment in single letter perception.

We present a theoretical account of letter-by-letter reading (LBL) that reconciles discrepant findings associated with this form of acquired dyslexia. We claim that LBL reading is caused by a deficit that affects the normal activation of the orthographic representation of the stimulus. In spite of this lower-level deficit, the degraded orthographic information may be processed further, and lexical, semantic, and higher-order orthographic information may still influence the reading patterns ofthese patients.In supportof our position, w e present a review of 57 published cases of LBL reading in w hich w e demonstrate that a peripheral deficit was evident in almost all of the patients and that, simultaneously, strong effects oflexical/ semantic variables were observed on reading performance. We then go on to report findings from an empirical analysis of seven LBL readers in whom w e document the joint effects of lexical variables (word frequency and im ageability) and word length on naming latency. We argue that the reading perform ance of these patients reflects the residual functioning of the same interactive system that supported normal reading premorbidly.

Most theoretical accounts of deep dyslexia postulate at least two independent deficits which give rise to the observed pattern of reading impairment. One deficit is an inability to derive phonology from orthography sublexically and the second is an impairment in semantically mediated reading. These deficits generate a host of symptoms including an impairment in reading nonwords, a part-of-speech and imageability effect in word reading, and, importantly, the occurrence of semantic paralexias. It is possible, then, that during recovery of deep dyslexia, either one or both of these underlying deficits resolve. We describe a case, RL, with deep dyslexia who showed significant change in his reading performance in the absence of any therapeutic intervention. At 18 months post-onset, unlike at 6 months post-onset, RL no longer produced any purely semantic errors nor did he show effects of imageability or past-of-speech on his oral readings. Despite his change, RL's ability to read nonwords did not impro...

A key issue that continues to generate controversy concerns the nature of the psychological, computational, and neural mechanisms that support the visual recognition of objects such as faces and words. While some researchers claim that visual recognition is accomplished by category-specific modules dedicated to processing distinct object classes, other researchers have argued for a more distributed system with only partially specialized cortical regions. Considerable evidence from both functional neuroimaging and neuropsychology would seem to favour the modular view, and yet close examination of those data reveals rather graded patterns of specialization that support a more distributed account. This paper explores a theoretical middle ground in which the functional specialization of brain regions arises from general principles and constraints on neural representation and learning that operate throughout cortex but that nonetheless have distinct implications for different classes of stimuli. The account is supported by a computational simulation, in the form of an artificial neural network, that illustrates how cooperative and competitive interactions in the formation of neural representations for faces and words account for both their shared and distinctive properties. We set out a series of empirical predictions, which are also examined, and consider the further implications of this account.

The dual route interpretation of surface dyslexia as a deficit in word-specific activation has been challenged recently by computational models that incorporate a unitary print-to-sound mechanism. The most current of these makes no allowance for word-specific nodes, but obtains the pronunciation of regular and exception words by weighted connections between graphemic and phonemic units. Damaging the model in a variety of ways produces a pattern that appears consistent with the performance of many surface dyslexic patients. Exception words are mispronounced more often than regular words, though accuracy deteriorates on both categories. In addition, frequency has no clear-cut effect on the probability of reading an exception word correctly. We describe the existence of a variant of the syndrome that is not fully captured by the above simulations. MP, a surface dyslexic, demonstrates a dissociation between lexical and nonlexical pronunciation of written words. We also show that performance on irregu...

In a previous paper, we proposed that patients with neglect dyslexia process information appearing on the unattended side. This information, if encoded sufficiently, may be used to trigger top-down knowledge, leading to the interaction of spatial attention and lexicality. The current studies examine this question in normal people. Subjects' attention was biased to the end of a letter string by a cue (underline bar) and lexical decisions were made to the underlined section of the letter string (for example, east and garm). These studies showed that reaction times were slower when distracting information appeared on the left than when no distractors were present (for example, arm). Furthermore, when the distractors played a lexical role and formed a word with the underlined string (for example, farm), lexical decisions were even slower. These results showed that distractors are processed at least to the level of lexical access and influence reading performance of the attended underlined string. We ...

A homophone retraining program was implemented with a surface dysgraphic patient. Extensive pre-therapy testing suggested that lexical processing was impaired in writing but not in reading, resulting in difficulties in writing homophones and irregular words. The treatment procedure involved the pairing of the written homophone with its pictorial representation in order to link the orthography with the corresponding meaning and to enhance direct lexical access. A series of exercises and practice techniques were introduced to strengthen this route. Results revealed significant improvement in writing treated homophones and untreated irregular words but minimal generalisation to untreated homophones. Theoretical explanations for the changes are offered and the efficacy of the treatment program is demonstrated.