Word length and orthographic neighborhood size effects in the left and right cerebral hemispheres

Previous studies have reported an interaction between visual field (VF) and word length such that word recognition is affected more by length in the left VF (LVF) than in the right VF (RVF). A reanalysis showed that the previously reported effects of length were confounded with orthographic neighborhood size (N). In three experiments we manipulated length and N in lateralized lexical decision tasks. Results showed that length and VF interacted even with N controlled (Experiment 1); that N affected responses to words in the LVF but not the RVF (Experiment 2); and that when length and N were combined, length only affected performance in the LVF for words with few neighbors.     

A left hemisphere, but not right hemispace, advantage for tactual simultaneity judgments

Hemispheric asymmetries for tactile simultaneity judgments were investigated in 34 dextral adults. Pairs of vibrotactile stimuli with simultaneous or successive onsets were delivered unilaterally to the left or right hand. Participants made a forced-choice, bipedal response, indicating whether a stimulus was simultaneous or successive. The effect of hemispatial attentional biases was investigated, using ipsilateral (arms uncrossed) and contralateral (arms crossed) hand placements. Trials presented to the right hand were associated with fewer errors and a trend for faster response times than were those presented to the left hand. There was no asymmetry in response bias. Manipulations of hemispace did not affect the right hand advantage. These results confirm the existence of a left hemisphere temporal-processing advantage but fail to demonstrate that the asymmetry is the result of a rightward attentional bias. The implications of these results for absolute and relative models of hemispheric specialization are discussed.     

Orthographic neighborhood size effects in recognition memory

This study argues for the importance of physical word features in recognition memory by investigating the influence of orthographic distinctiveness. Experiment 1 demonstrated a mirror effect in ayes/no recognition test by manipulating orthographic neighborhood size. Words with small neighborhoods showed more hits and fewer false alarms than did words with larger neighborhoods. Experiment 2 replicated the neighborhood size mirror effect using null pairs in a forced choice recognition test. Experiment 3 required remember/know judgments in a yes/no recognition task. Experiment 4 used the same yes/no test as did Experiment 1, adding a study task that drew attention away from orthographic information in the study list. The mirror pattern disappeared with the addition of the study task.     

Orthographic neighborhood effects in lexical decision: the effects of nonword orthographic neighborhood size

The effects of large neighborhoods (neighborhood size) and of higher frequency neighbors (neighborhood frequency) were examined as a function of nonword neighborhood size in lexical decision tasks. According to the multiple read-out model (J. Grainger & A. M. Jacobs, 1996), neighborhood size and neighborhood frequency effects should vary systematically as a function of nonword neighborhood size. In these experiments, the nonword context was more extensively manipulated than in previous studies, providing a more complete test of the model's predictions. In addition, simulations were conducted examining the model's ability to account for the facilitatory neighborhood size and neighborhood frequency effects observed in these experiments. The results suggest that the model overestimates the role of inhibition in the orthographic processing of English words.     

Orthographic neighborhood and concreteness effects in the lexical decision task

The experiment reported here investigated the sensitivity of concreteness effects to orthographic neighborhood density and frequency in the visual lexical decision task. The concreteness effect was replicated with a sample of concrete and abstract words that were not matched for orthographic neighborhood features and in which concrete words turned out to have a higher neighborhood density than abstract words. No consistent effect of concreteness was found with a sample of concrete and abstract words matched for orthographic neighborhood density and frequency and having fewer neighbors and higher-frequency neighbors than the words of the first sample. Post hoc analyses of the results showed that orthographic neighborhood density was not a nuisance variable producing a spurious effect of concreteness but, instead, that the existence of higher-frequency neighbors constitutes a necessary condition for concreteness effects to appear in the lexical decision task. This finding is consistent with the hypothesis that semantic information is accessed and used to generate the responses in lexical decision when inhibition from orthographic forms delays the target word recognition.     

Homotopic language reorganization in the right hemisphere after early left hemisphere injury

Speech production is inextricably linked to speech perception, yet they are usually investigated in isolation. In this study, we employed a verbal-repetition task to identify the neural substrates of speech processing with two ends active simultaneously using functional MRI. Subjects verbally repeated auditory stimuli containing an ambiguous vowel sound that could be perceived as either a word or a pseudoword depending on the interpretation of the vowel. We found verbal repetition commonly activated the audition-articulation interface bilaterally at Sylvian fissures and superior temporal sulci. Contrasting word-versus-pseudoword trials revealed neural activities unique to word repetition in the left posterior middle temporal areas and activities unique to pseudoword repetition in the left inferior frontal gyrus. These findings imply that the tasks are carried out using different speech codes: an articulation-based code of pseudowords and an acoustic-phonetic code of words. It also supports the dual-stream model and imitative learning of vocabulary.     

Form-specific visual priming in the right cerebral hemisphere.

Results of 4 experiments indicate that both within-modality and case-specific visual priming for words are greater when test stimuli are presented initially to the right cerebral hemisphere (RH). In contrast, neither within-modality nor case-specific explicit memory for words is greater when stimuli are presented initially to the RH. Priming is measured using word-stem completion, and explicit memory is measured using word-stem cued recall. In both cases, Ss first rate how much they like words, and then word stems are presented briefly to the RH (in the left visual field) or to the left hemisphere (in the right visual field). Results suggest that at least 2 separate systems encode the visual representations that produce priming. The system that is more effective in the RH is better at representing form-specific information, whereas another system that is not more effective in the RH does not distinguish among distinct instances of word forms.     

Children like dense neighborhoods: Orthographic neighborhood density effects in novel readers

Previous evidence with English beginning readers suggests that some orthographic effects, such as the orthographic neighborhood density effects, could be stronger for children than for adults. Particularly, children respond more accurately to words with many orthographic neighbors than to words with few neighbors. The magnitude of the effects for children is much higher than for adults, and some researchers have proposed that these effects could be progressively modulated according to reading expertise. The present paper explores in depth how children from 1st to 6th grade perform a lexical decision with words that are from dense or sparse orthographic neighborhoods, attending not only to accuracy measures, but also to response latencies, through a computer-controlled task. Our results reveal that children (like adults) show clear neighborhood density effects, and that these effects do not seem to depend on reading expertise. Contrarily to previous claims, the present work shows that orthographic neighborhood effects are not progressively modulated by reading skill. Further, these data strongly support the idea of a general language-independent preference for using the lexical route instead of grapheme-to-phoneme conversions, even in beginning readers. The implications of these results for developmental models in reading and for models in visual word recognition and orthographic encoding are discussed.     

When left means right: an explanation of the left cradling bias in terms of right hemisphere specializations

Previous research has indicated that 70-85% of women and girls show a bias to hold infants, or dolls, to the left side of their body. This bias is not matched in males (e.g. deChateau, Holmberg & Winberg, 1978; Todd, 1995). This study tests an explanation of cradling preferences in terms of hemispheric specialization for the perception of facial emotional expression. Thirty-two right-handed participants were given a behavioural test of lateralization and a cradling task. Females, but not males, who cradled a doll on the left side were found to have significantly higher laterality quotients than right cradlers. Results indicate that women cradle on the side of the body that is contralateral to the hemisphere dominant for face and emotion processing and suggest a possible explanation of gender differences in the incidence of cradling.     

Contextual mood priming following left and right hemisphere damage

This research examined the influence of mood-congruent and mood-incongruent contexts on recognizing affective prosody after brain damage. Predictions stemmed from an associative network theory of learning and memory. Thirty-three male subjects, 11 each in right hemisphere damaged (RHD), left hemisphere damaged (LHD), and normal control groups judged moods from the prosody of semantically neutral phrases. In one task, the prosodic stimulus phrases were judged in isolation. In another task, the phrases were preceded by short paragraphs which were either congruent or incongruent in emotional tone with the prosodic stimuli. These paragraphs were designed to prime specific mood choices. As anticipated, LHD subjects' prosodic mood recognition was more accurate when given congruent rather than incongruent affective contexts. Congruent contexts facilitated, and incongruent contexts disrupted, their prosodic mood judgments to the same extent as normals. RHD subjects showed a partial context decrement. They were less accurate than normal or LHD subjects in the congruent condition, and were unaffected by incongruent contexts. When given congruent biasing paragraphs, however, RHD subjects did experience facilitation on a par with that found for the other groups, indicating spared sensitivity to certain contextual factors. The distinction between automatic and effortful processes is offered as a potential explanation for the RHD group's pattern of performance.     

Form-specific visual priming for new associations in the right cerebral hemisphere

In three experiments, we examined the internal processing mechanisms of relatively independent visual-form subsystems. Participants first viewed centrally presented word pairs and then completed word stems presented beneath context words in the left or right visual field. Letter-case-specific priming in stem completion was found only when the context word was the same word that had previously appeared above the primed completion word and the items were presented directly to the right cerebral hemisphere. This pattern of results was not found when participants deliberately recollected previously presented words when completing the stems. Results suggest that holistic processing, not parts-based processing as assumed in many contemporary theories of visual-form recognition, is performed in a subsystem that distinguishes specific instances in the same abstract category of form and that operates more effectively in the right hemisphere than in the left hemisphere.     

Left hemisphere sensitivity to consonant sounds not displayed by the right hemisphere: electrophysiological correlates

Auditory evoked responses (AER) to a series of consonant-vowel syllables were recorded from frontal, temporal, and parietal scalp locations from 14 right-handed college students. Averaged AERs were submitted to principal components analysis and analysis of variance. Six components of the group's AERs were found to reflect various aspects of the stimulus parameters. One component reflected changes over only the left hemisphere to different consonants. A second component changed systematically over both hemispheres but did not discriminate between all consonants.     

Imagery and verbal encoding in left and right hemisphere damaged patients

Neuropsychological aspects of imaginal and verbal encoding in memory were explored in two forced-choice recognition memory experiments with patients suffering from left and right anterior cerebral hemisphere damage. In the first experiment stimulus type and rate of presentation were varied. Predictions of patient performance based on the hypothesis that left anterior hemisphere pathology impairs verbal memory coding and right anterior hemisphere pathology impairs imaginal coding were confirmed. In a second recognition memory experiment for pictures of common objects, system-specific (imaginal or verbal) interference and distractor effects were demonstrated by analyzing the effects of interpolated tasks and the nature of false-recognition errors.     

Remembering 1500 pictures: the right hemisphere remembers better than the left

We hypothesized that the right hemisphere would be superior to the left hemisphere in remembering having seen a specific picture before, given its superiority in perceptually encoding specific aspects of visual form. A large set of pictures (N=1500) of animals, human faces, artifacts, landscapes, and art paintings were shown for 2s in central vision, or tachistoscopically (for 100ms) in each half visual field, to normal participants who were then tested 1-6 days later for their recognition. Images that were presented initially to the right hemisphere were better recognized than those presented to the left hemisphere. These results, obtained with participants with intact brains, large number of stimuli, and long retention delays, are consistent with previously described hemispheric differences in the memory of split-brain patients.     

When only the right hemisphere is left: studies in language and communication

An adult of above normal intelligence, BL, underwent left hemispherectomy at age five, and subsequently graduated from college and has been regularly employed. Using standardized neuropsychological instruments, previous extensive testing had revealed optimal performance for a hemispherectomized subject. To probe communicative abilities in greater detail, and to examine current questions about linguistic superiority of the left hemisphere and "crowding" of right hemisphere functions, 12 additional protocols were administered. BL performed at normal or above on nearly all protocols. However, performance on production of phonemically complex words was effortful, and deficits were seen on two tests requiring comprehension of linguistic contrasts in prosody (Linguistic Prosody Test) and syntax (the Active-Passive Test). These findings support previous claims of reduced ability in specific, circumscribed linguistic functions in the left hemispherectomized person, and lead to suggestions for further testing of communicative competence in individuals with a single intact hemisphere.     

Lexical decisions in the right and left cerebral hemispheres

Subjects performed a lexical decision task in which letter-strings were presented unilaterally and tachistoscopically to the right and left visual fields. Four types of letter-strings were used: high frequency words, low frequency words, pronounceable nonwords, and unpronounceable nonwords. Measures of reaction time and error rate both showed a right visual field advantage for both classes of words and no difference between the hemispheres for either class of nonword. It was concluded that meaning is a more salient parameter of wordness than is pronounceability. Possible mechanisms for processing words presented to the left visual field were discussed.     

Superiority of the left cerebral hemisphere in word recognition with nonverbal central fixation

The right visual-field advantage for bilateral presentation put forward by McKeever and Huling was investigated. The central-fixation task was varied so that in one condition this task was nonverbal. Results gave some support for scanning-type explanations in this paradigm but over-all favoured Kinsbourne's activation-and-priming account.     

Probability matching in the right hemisphere

Previously it has been shown that the left hemisphere, but not the right, of split-brain patients tends to match the frequency of previous occurrences in probability-guessing paradigms (Wolford, Miller, & Gazzaniga, 2000). This phenomenon has been attributed to an "interpreter," a mechanism for making interpretations and forming hypotheses, thought to reside exclusively in the left hemisphere. In this study with a split-brain patient, we had him guess one of two types of faces, stimuli known to be preferentially processed in the right hemisphere of this patient. Unlike previous studies using other kinds of stimuli, the right hemisphere matched the frequency of the previous occurrences of a face-type, but the left hemisphere did not.