Effects of typeface characteristics on visual field asymmetries for letter identification in children and adults

What differs in visual recognition of handwritten vs. printed letters? An fMRI study

In models of letter recognition, handwritten letters are considered as a particular font exemplar, not qualitatively different in their processing from printed letters. Yet, some data suggest that recognizing handwritten letters might rely on distinct processes, possibly related to motor knowledge. We applied functional magnetic resonance imaging to compare the neural correlates of perceiving handwritten letters vs. standard printed letters. Statistical analysis circumscribed to frontal brain regions involved in hand-movement triggering and execution showed that processing of handwritten letters is supported by a stronger activation of the left primary motor cortex and the supplementary motor area. At the whole-brain level, additional differences between handwritten and printed letters were observed in the right superior frontal, middle occipital, and parahippocampal gyri, and in the left inferior precentral and the fusiform gyri. The results are suggested to indicate embodiment of the visual perception of handwritten letters.

Reading words, seeing style: the neuropsychology of word, font and handwriting perception

The reading of text is predominantly a left hemisphere function. However, it is also possible to process text for attributes other than word or letter identity, such as style of font or handwriting. Anecdotal observations have suggested that processing the latter may involve the right hemisphere. We devised a test that, using the identical stimuli, required subjects first to match on the basis of word identity and second to match on the basis of script style. We presented two versions, one using various computer fonts, and the other using the handwriting of different individuals. We tested four subjects with unilateral lesions who had been well characterized by neuropsychological testing and structural and/or functional MRI. We found that two prosopagnosic subjects with right lateral fusiform damage eliminating the fusiform face area and likely the right visual word form area were impaired in completion times and/or accuracy when sorting for script style, but performed better when sorting for word identity. In contrast, one alexic subject with left fusiform damage showed normal accuracy for sorting by script style and normal or mildly elevated completion times for sorting by style, but markedly prolonged reading times for sorting by word identity. A prosopagnosic subject with right medial occipitotemporal damage sparing areas in the lateral fusiform gyrus performed well on both tasks. The contrast in the performance of patients with right versus left fusiform damage suggests an important distinction in hemispheric processing that reflects not the type of stimulus but the nature of processing required.

Abstraction and perceptual individuation in primed word identification are modulated by distortion and repetition: a dissociation

One experiment investigated the effects of distortion and multiple prime repetition (super-repetition) on repetition priming using divided-visual-field word identification at test and mixed-case words (e.g., goAT). The experiment measured form-specificity (the effect of matching lettercase at study and test) for two non-conceptual study tasks. For an ideal typeface, super-repetition increased form-independent priming leaving form-specificity constant. The opposite pattern was found for a distorted typeface; super-repetition increased form-specificity, leaving form-independent priming constant. These priming effects did not depend on the study task or test hemifield for either typeface. An additional finding was that only the ideal typeface showed the usual advantage of right hemifield presentation. These results demonstrate that super-repetition produced abstraction for the ideal typeface and perceptual individuation for the distorted typeface; abstraction and perceptual individuation dissociated. We suggest that there is a fundamental duality between perceptual individuation and abstraction consistent with Tulving's (1984) distinction between episodic and semantic memory. This could reflect a duality of system or process.

What do lateralized displays tell us about visual word perception? A cautionary indication from the word-letter effect

A common assumption underlying laterality research is that visual field asymmetries in lateralized word perception indicate the hemispheric specialisation of processes generally available for the perception of words, including words viewed in a more typical setting (i.e. in the central visual field). We tested the validity of this assumption using a phenomenon (the word-letter effect) frequently reported for displays viewed in the central visual field, where letters in words are perceived more accurately than the same letters in isolation. Words and isolated letters were presented in the left visual field (LVF), right visual field (RVF) and central visual field (CVF), the Reicher-Wheeler task was used to suppress influences of guesswork, and an eye-tracker ensured central fixation. In line with previous findings, lateralized displays revealed a RVF-LVF advantage for words (but not isolated letters) and CVF displays revealed an advantage for words over isolated letters (the word-letter effect). However, RVF and LVF displays both produced an advantage for isolated letters over words (a letter-word effect), indicating that processing subserving the advantage for words when participants viewed stimuli in the central visual field was unavailable for lateralized displays. Implications of these findings for studies of lateralized word perception are discussed.

The left visual hemispace bias for the perception of chimeric faces: a further test of the difficulty of discrimination hypothesis

When people make judgments of visual-spatial forms, they generally perform better if the information is presented in their left visual hemispace (LVH), whereas for verbal material, they generally show a right visual hemispace (RVH) bias. For verbal material, the strength and direction of the effect also has been linked to task difficulty, with the bias shifting toward the RVH as task difficulty increases. Two experiments are presented that show the reverse direction of change for a nonverbal task; that is, when a nonverbal task is more difficult, the usual LVH effect shifts toward an RVH bias. Taking into account recent developments in theory and research on hemispheric differences in styles of information processing, we propose that task difficulty is related more generally to changes in processing style.

Visuographemic alexia: a new form of a peripheral acquired dyslexia

We report a single-case study of peripherally acquired dyslexia that meets the clinical criteria of "alexia without agraphia." The patient, AA, has a large infarct involving the left posterior cerebral artery. The most striking feature is a severe impairment in recognizing single visually presented letters that precludes explicit or implicit access to reading, even in a letter-by-letter fashion. AA can, however, differentiate letters from similar nonsense characters and digits, and he is also able to identify alphanumeric signs when the visual channel is bypassed (through somesthesic or kinesthesic presentation). Spelling tasks are also well performed. Since there is a breakdown in mapping a visually presented letter to its abstract graphemic representation, we propose the term "visuographemic alexia" for this kind of reading disorder. The pattern of deficits is interpreted following theoretical models previously developed in cognitive neuropsychology. An alexia for arabic numerals with preserved comprehension lends additional support for the crucial processing of different notational systems (e.g., phonographic vs logographic). More general perceptive disorders do not seem to account for these patterns; they are material-specific. Finally, we attempt to specify functional correlations with the implied neural networks.

Central fixations are inadequately controlled by instructions alone: implications for studying cerebral asymmetry

A fundamental concern when using visual presentations to study cerebral asymmetry is to ensure that stimuli are presented with the same degree of retinal eccentricity from a central fixation point in either visual field. However, a widely used procedure intended to control fixation location merely instructs participants to fixate appropriately without any other means of ensuring that central fixations actually occur. We assessed the validity of assuming that instructions alone ensure central fixation by using the traditional RVF advantage for words and either (a) only instruction to fixate centrally, or (b) eye-tracking device that ensured central fixation on every trial. Experiments 1 and 2 found that when only instructions were given, the vast majority of fixations were not central, and more occurred to the right of centre than to the left. Moreover, the prevalence of non-central fixations was otherwise disguised by the finding that both fixation procedures produced similar RVF advantages in overt performance. The impact of typical non-central fixations on performance was revealed by systematically manipulating fixation location in Experiment 3, where deviations in fixation of only 0.25 degrees from centre had a reliable impact on visual field effects. Implications of these findings for studies of cerebral asymmetry are discussed.