Charlotte Hills

The word-length effect in reading: A review

The finding that visual processing of a word correlates with the number of its letters has an extensive history. In healthy subjects, a variety of methods, including perceptual thresholds, naming and lexical decision times, and ocular motor parameters, show modest effects that interact with high-order effects like frequency. Whether this indicates serial processing of letters under some conditions or indexes low-level visual factors related to word length is unclear. Word-length effects are larger in pure alexia, where they probably reflect a serial letter-by-letter strategy, due to failure of lexical whole-word processing and variable dysfunction in letter encoding. In pure alexia, the word-length effect is systematically related to mean naming latency, with the word-length effect becoming proportionally greater as naming latency becomes more delayed in severe cases. Other conditions may also generate enhanced word-length effects. This occurs in right hemianopia: Computer simulations suggest a criterion of 160 ms/letter to distinguish hemianopic dyslexia from pure alexia. Normal reading development is accompanied by a decrease in word-length effects, whereas persistently elevated word-length effects are characteristic of developmental dyslexia. Little is known about word-length effects in other reading disorders. We conclude that the word-length effect captures the efficiency of the perceptual reading process in development, normal reading, and a number of reading disorders, even if its mechanistic implications are not always clear.

Voice Recognition in Face-Blind Patients.

Right or bilateral anterior temporal damage can impair face recognition, but whether this is an associative variant of prosopagnosia or part of a multimodal disorder of person recognition is an unsettled question, with implications for cognitive and neuroanatomic models of person recognition. We assessed voice perception and short-term recognition of recently heard voices in 10 subjects with impaired face recognition acquired after cerebral lesions. All 4 subjects with apperceptive prosopagnosia due to lesions limited to fusiform cortex had intact voice discrimination and recognition. One subject with bilateral fusiform and anterior temporal lesions had a combined apperceptive prosopagnosia and apperceptive phonagnosia, the first such described case. Deficits indicating a multimodal syndrome of person recognition were found only in 2 subjects with bilateral anterior temporal lesions. All 3 subjects with right anterior temporal lesions had normal voice perception and recognition, 2 of whom performed normally on perceptual discrimination of faces. This confirms that such lesions can cause a modality-specific associative prosopagnosia.

Word and text processing in acquired prosopagnosia.

A novel hypothesis of object recognition asserts that multiple regions are engaged in processing an object type, and that cerebral regions participate in processing multiple types of objects. In particular, for high‐level expert processing, it proposes shared rather than dedicated resources for word and face perception, and predicts that prosopagnosic subjects would have minor deficits in visual word processing, and alexic subjects would have subtle impairments in face perception. In this study, we evaluated whether prosopagnosic subjects had deficits in processing either the word content or the style of visual text.

Seeing the eyes in acquired prosopagnosia.

Case reports have suggested that perception of the eye region may be impaired more than that of other facial regions in acquired prosopagnosia. However, it is unclear how frequently this occurs, whether such impairments are specific to a certain anatomic subtype of prosopagnosia, and whether these impairments are related to changes in the scanning of faces. We studied a large cohort of 11 subjects with this rare disorder, who had a variety of occipitotemporal or anterior temporal lesions, both unilateral and bilateral. Lesions were characterized by functional and structural imaging. Subjects performed a perceptual discrimination test in which they had to discriminate changes in feature position, shape, or external contour. Test conditions were manipulated to stress focused or divided attention across the whole face. In a second experiment we recorded eye movements while subjects performed a face memory task. We found that greater impairment for eye processing was more typical of subjects with occipitotemporal lesions than those with anterior temporal lesions. This eye selectivity was evident for both eye position and shape, with no evidence of an upper/lower difference for external contour. A greater impairment for eye processing was more apparent under attentionally more demanding conditions. Despite these perceptual deficits, most subjects showed a normal tendency to scan the eyes more than the mouth. We conclude that occipitotemporal lesions are associated with a partially selective processing loss for eye information and that this deficit may be linked to loss of the right fusiform face area, which has been shown to have activity patterns that emphasize the eye region.

Perceptual learning of faces: A rehabilitative study of acquired prosopagnosia

Despite many studies of acquired prosopagnosia, there have been only a few attempts at its rehabilitation, all in single cases, with a variety of mnemonic or perceptual approaches, and of variable efficacy. In a cohort with acquired prosopagnosia, we evaluated a perceptual learning program that incorporated variations in view and expression, which was aimed at training perceptual stages of face processing with an emphasis on ecological validity. Ten patients undertook an 11-week face training program and an 11-week control task. Training required shape discrimination between morphed facial images, whose similarity was manipulated by a staircase procedure to keep training near a perceptual threshold. Training progressed from blocks of neutral faces in frontal view through increasing variations in view and expression. Whereas the control task did not change perception, training improved perceptual sensitivity for the trained faces and generalized to new untrained expressions and views of those faces. There was also a significant transfer to new faces. Benefits were maintained over a 3-month period. Training efficacy was greater for those with more perceptual deficits at baseline. We conclude that perceptual learning can lead to persistent improvements in face discrimination in acquired prosopagnosia. This reflects both acquisition of new skills that can be applied to new faces as well as a degree of overlearning of the stimulus set at the level of 3-D expression-invariant representations.

Visual word expertise: a study of inversion and the word-length effect, with perceptual transforms.

The word-length effect may indicate whether reading is proceeding in an efficient whole-word fashion or by serial letter processing. If it is an index of an orientation-dependent expert reading mechanism, then it should show an inversion effect, with a large difference between upright and upside-down text that is specific for normally configured text. We measured response time of healthy subjects reading 3- to 9-letter words presented in normal configuration, in mirror reflection or spelt backward, in either upright or inverted orientation. The word-length effect showed an inversion effect specific for normal text, as it was not seen for either backward or mirrored text, a result that differed from that for simple mean response times. Also, the word-length effect was smaller for backward than for mirrored text, suggesting that reading of transformed text uses primarily local letters rather than global word forms. We conclude that the word-length effect is a suitable index of expert reading, and reveals that reading under perceptually difficult conditions relies on a sublexical letter-based strategy.

An adaptation study of internal and external features in facial representations

Prior work suggests that internal features contribute more than external features to face processing. Whether this asymmetry is also true of the mental representations of faces is not known. We used face adaptation to determine whether the internal and external features of faces contribute differently to the representation of facial identity, whether this was affected by familiarity, and whether the results differed if the features were presented in isolation or as part of a whole face. In a first experiment, subjects performed a study of identity adaptation for famous and novel faces, in which the adapting stimuli were whole faces, the internal features alone, or the external features alone. In a second experiment, the same faces were used, but the adapting internal and external features were superimposed on whole faces that were ambiguous to identity. The first experiment showed larger aftereffects for unfamiliar faces, and greater aftereffects from internal than from external features, and the latter was true for both familiar and unfamiliar faces. When internal and external features were presented in a whole-face context in the second experiment, aftereffects from either internal or external features was less than that from the whole face, and did not differ from each other. While we reproduce the greater importance of internal features when presented in isolation, we find this is equally true for familiar and unfamiliar faces. The dominant influence of internal features is reduced when integrated into a whole-face context, suggesting another facet of expert face processing.