Form-specific priming and functional brain asymmetries in perceptual identification

Word form representations in intact cerebral hemispheres were studied by a lateralized perceptual identification priming task. During the study phase, word forms were primed by displaying words visually in uppercase or lowercase letters. During the test phase, perceptual identification of non-studied baseline words and studied words (presented in same or different lettercase as studied) was tested by displaying targets in the left or right visual field. Experiment 1 showed that the hemispheric pattern of priming effects was dependent on the lettercase at test. For uppercase test items, only the left visual field/right hemisphere was sentitive to study-test changes in lettercase, replicating an earlier result obtained in word-stem completion (Marsolek, Kosslyn and Squire, 1992). However, lowercase test items did not reveal any asymmetries in the form-dependent priming component indicating that in some conditions form-specific representations are computed in the left hemisphere also. No asymmetries were found in the abstract, form-independent component of priming. Experiment 2 revealed that use of explicit memory in the perceptual identification task eliminated the form-specific priming effects and suggested that the results of Experiment 1 were uncontaminated by explicit memory.     

Effects of stimulus arrangement on hemispheric differences and interhemispheric interaction for processing letter trigrams.

Observers identified consonant-vowel-consonant (CVC) nonsense syllables with the letters arranged horizontally. In each of 2 experiments, there were fewer errors when stimuli were presented to the right visual field (RVF) and left hemisphere (LH) than when stimuli were presented to the left visual field (LVF) and right hemisphere (RH), and the extent to which the number of last-letter errors exceeded the number of first-letter errors was greater on LVF/RH than on RVF/LH trials. When the same stimulus was presented simultaneously to both visual fields (Experiment 2), the qualitative error pattern was very similar to the pattern obtained on LVF/RH trials. These effects replicate results obtained in earlier CVC identification experiments with letters arranged vertically. However. when a single stimulus was presented in the center of the visual field (Experiment 1), so that the first letter of the CVC projected to the LVF/RH and the last letter projected to the RVF/LH, the error pattern was a mixture of the LVF/RH and RVF/LH patterns, as if each hemisphere took the lead for processing the letter it received directly. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Detecting targets in letter and non-letter arrays.

Three experiments with 48 right-handed undergraduates examined the difference between the processing of letter and nonletter arrays using visual search. Results show that (1) letters were processed differently from other shapes; specifically, detection latencies were relatively short for the ends of letter arrays and increased left to right yielding a sloping M-shaped function, whereas the function for nonletter arrays was U-shaped; (2) this result was not restricted to any one nonletter character set, nor is visual familiarity or nameability crucial; and (3) digits produced results comparable to letters. Mechanisms common to word and number processing are advanced to account for this latter finding. The basic letter–shape contrast shows that the letter position function is constrained by processing strategy, not by structural limitations. (French abstract) (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some temporal characteristics of processing during reading.

14 college students read passages displayed on a CRT as their eye movements were being monitored. During occasional fixations, all letters to the left of the directly fixated letter or all letters more than 4 to the right of the fixated letter were replaced by other letters. This replacement occurred either for only the 1st 100 msec of the fixation or only after the 1st 100 msec of the fixation. Eye movement data indicate that the eyes could respond to change in the visual stimulus within less than 100 msec and to orthographic irregularity in the test within less than 160 msec. No evidence was found for a left-to-right attentional scan during a fixation. Results are interpreted within the framework of a chronology of processing events occurring during a fixation in reading. Eye movement patterns and the determination of fixation durations are discussed. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hierarchical control and skilled typing: Evidence for word-level control over the execution of individual keystrokes.

Routine actions are commonly assumed to be controlled by hierarchically organized processes and representations. In the domain of typing theories, word-level information is assumed to activate the constituent keystrokes required to type each letter in a word. We tested this assumption directly using a novel single-letter probe technique. Subjects were primed with a visual or auditory word or a visually presented random consonant string and then probed to type a single letter from the prime or another randomly selected letter. Relative to randomly selected letters, probe responses were speeded for first, middle, and last letters contained in visual and auditory word primes but not for middle and last letters contained in random consonant primes. This suggests that word-level information causes parallel activation of constituent keystrokes, consistent with hierarchical processing. The role of hierarchical processing in typing and routine action is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Order of processing in visual perception.

Three experiments tested predictions derived from 3 cognitive scanning hypotheses proposing respectively a left-to-right, ends-first, and peripheral-foveal order of scanning. In Exps I and II configurations of letters and/or digits were presented to 11 Ss around a central fixation point, and the stimulus was followed by a 1-sec presentation of a patterned mask or a blank white field. Backward masking selectively impaired the identification of stimuli in foveal positions whether or not these stimuli occupied middle-of-row positions. In Exp III 4 Ss made a manual same-different response to the presence or absence of a critical letter presented 3Deg. to the left or right of fixation. Noise letters appeared on either side or both sides of the critical letter. Identification response times were faster when the critical letter appeared in the left-most position in left field arrays and the right-most position in right field arrays. Principal conclusions drawn from the 3 experiments were: (a) Alphanumeric stimuli are scanned from the peripheral visual field inward towards fixation. (b) Any left-to-right scanning occurs relatively late in iconic processing. (c) An ends-first scanning strategy is a particular case of a more general peripheral-foveal strategy. (French summary) (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation of letter and picture naming resulting from callosal disconnection

BACKGROUND: Detailed mapping of the corpus callosum for functional fractionation in humans remains incomplete. OBJECTIVE: To examine separable interhemispheric transfer of visual information by callosal fibers, especially in the splenium. METHODS: We examined callosal disconnection signs in a 14-year-old boy with a lesion confined to the posterior part of the splenium and reviewed reported cases with callosal lesions. RESULTS AND CONCLUSION: The patient presented with left hemialexia as the only manifestation of callosal disconnection syndrome. The only difficulty demonstrated was in reading aloud or copying letters, which were presented tachistoscopically to the left visual field, with his right hand. He could copy letters presented to his left visual field with his left hand, however. Therefore, left hemialexia was not due to hemiamblyopia or hemineglect. There was no anomia for pictures and colors in the left visual field. MRI revealed that the lesion was limited to the ventroposterior end of the splenium. Review of 40 reported patients with callosal lesions suggests that the anterior to middle part of the splenium is involved in transferring picture information from the language-nondominant hemisphere to the language-dominant hemisphere and that the ventroposterior part is involved in transferring letter information.     

Image generation and processing of generated images in the cerebral hemispheres.

Recent computational models describing the contribution of the cerebral hemispheres to visual imagery have suggested an exclusive capacity of the left hemisphere to generate multipart images. A brief review of relevant findings indicates that the evidence presented in support of this suggestion is not entirely compelling; this prompted a reexamination of this issue in a lateral tachistoscopic study on normal adults. Sixteen subjects participated in two experiments in which they had to decide whether or not a lowercase letter contained a segment extending above or below the main body of the letter. This decision was made directly on lowercase letters in one experiment (perceptual task) and on their generated images in the other experiment (imagery task). The quality of the letters (clear or blurred) and the retinal eccentricity of stimulus presentation (small or large) were orthogonally manipulated. The perceptual task yielded no main effect of visual field but a significant interaction of visual field and letter quality. By contrast, the imagery task resulted in a left visual-field superiority but no interaction involving the visual fields—a departure from predictions based on current models of visual imagery. In addition, the pattern of results in the imagery task corresponded to that obtained with blurred letters in the perceptual task, suggesting limitations in spatial resolution of visual images. Implications of these results for models of cerebral lateralization and visual imagery are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Form-specific explicit and implicit memory in the right cerebral hemisphere.

Results from 2 divided visual field (DVF) experiments indicate that in some conditions both explicit and implicit memory are greater when same-letter-case stimuli are presented directly to the right cerebral hemisphere (in the left visual field) than when they are presented directly to the left (in the right visual field). Explicit memory was measured with word-stem cued recall, and implicit memory was measured with word-stem completion priming. Words were presented centrally during encoding, and word stems were presented directly to the right hemisphere or to the left hemisphere during testing. Results for explicit memory contrast with findings from a previous DVF study that used a different procedure, those for implicit memory replicate previous DVF findings, and both results corroborate positron emission tomography findings. It is suggested that a form-specific system in the right hemisphere may contribute to both explicit and implicit memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Right visual field superiority for letter recognition with partial report.

Experiments using partial report techniques have typically failed to find left-right visual field differences in the recognition of tachistoscopically presented letter rows. Such data represent a difficulty for theories that emphasize the relevance of cerebral hemispheric asymmetry. It is contended that the end items of a display are critical, and that a truly symmetric display should have both a left and a right end item in each visual field. In the present experiments with 36 righthanded university students, partial report procedures were employed, but a gap was placed between the left and right halves of the display. In the 1st experiment, a single-letter spatial probe procedure was used, and a clear right visual field superiority was found. In the 2nd experiment, a hemifield report procedure was used; the presence of a gap in the display enhanced the right visual field superiority, especially for shorter strings of letters. Results indicate that right visual field superiority can be obtained with partial report procedures under appropriate conditions. (French summary) (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The roles of stimulus-response compatibility and mental rotation in mirror-image and left-right decisions.

Examined the relative roles of mental rotation and stimulus-response (SR) compatibility in mirror-image and left-right decisions. 15 Ss, aged 19–43 yrs, were shown rotated letters and asked to indicate whether the letters were normal or backward (mirror-image task). Ss were then asked whether a dot would be located to the left or right of each letter if the letter was upright (viewer-centered left-right task) or if the letter was both upright and normal (letter-centered left-right task). The functions relating reaction time (RT) to angular orientation were parallel across the 3 tasks, suggesting that SR compatibility played no role, and that the Ss mentally rotated the letters to the upright in each case. A marked increase in RT to backward letters in the letter-centered task suggested a 2nd rotation in depth to restore the letters to normal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Infectious causes of atherosclerosis

Brain imaging studies have suggested a critical role for prefrontal cortex in working memory (WM) tasks that require both maintainenance and manipulation of information over time in delayed-response WM tasks. In the present study, functional magnetic resonance imaging (fMRI) was used to examine whether prefrontal areas are activated when only maintenance is required in a delayed-response WM task, without the overt requirement to manipulate the stored information. In two scans, six subjects performed WM tasks in which, on each trial, they (1) encoded 1, 3, or 6 to-be-remembered letters, (2) maintained these letters across a 5-second unfilled delay, and (3) determined whether a single probe letter was or was not part of the memory set. Activation of left caudal inferior frontal gyrus was observed, relative to the 1-letter task, when subjects were required to maintain 3 letters in WM. When subjects were required to maintain 6 letters in WM, additional prefrontal areas, most notably middle and superior frontal gyri, were activated bilaterally. Thus, increasing the amount of to-be-maintained information, without any overt manipulation requirement, resulted in the recruitment of wide-spread frontal-lobe regions. Inferior frontal gyrus activation was left-hemisphere dominant in both the 3- and 6-letter conditions, suggesting that such activation reflected material-specific verbal processes. Activation in middle and superior frontal gyri appeared only in the 6-letter condition and was right-hemisphere dominant, suggesting that such activation reflected material-independent executive processes.     

Memory for position and identity across eye movements.

Used a "transsaccadic" partial report procedure to measure memory for position and identity information across saccades. Delaying the partial-report cue after the eye movement had little effect on report accuracy. Mask presentation hindered recall only at the shortest delay. Accuracy was much higher when the letter array contained 6 letters than when it contained 10 letters. Intra-array errors were much more frequent than extra-array errors. These results suggest that memory across eye movements decays slowly, has a limited capacity, is maskable for a brief time, and retains identity information better than position information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Orthography and the Hemispheres: Visual and Linguistic Aspects of Letter Processing.

Hebrew and Arabic are Semitic languages with a similar morphological structure and orthographies that differ in visual complexity. Two experiments explored the interaction of the characteristics of orthography and hemispheric abilities on lateralized versions of a letter-matching task (Experiment 1) and a global-local task (Experiment 2). In Experiment 1, native Hebrew readers and native Arabic readers fluent in Hebrew matched letters in the 2 orthographies. The results support the hypothesis that Arabic orthography is more difficult than Hebrew orthography for participants who can read both languages and that this difficulty has its strongest effects in the left visual field. In Experiment 2, native Arabic speakers performed a global-local letter detection task with Arabic letters with 2 types of inconsistent stimuli: different and similar. The results support the hypothesis that the right hemisphere of skilled Arabic readers cannot distinguish between similar Arabic letters, whereas the left hemisphere can. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pointage d'une position mémorisée et contexte visuel.

Determined whether a sensorimotor or cognitive encoding is used to encode a target position and save it into iconic memory. The methodology consisted of disrupting a manual aiming movement to a memorized visual target by displacing the visual field containing the target. The target was presented either centrally or in the right periphery. Participants moved their hand from the left to the right of fixation. The visual field was either stationary throughout the trial or was displaced to the right or left at the extinction of the target or at the start of the hand movement. Results showed three major effects: (1) Vision of the hand during the gesture improved the final accuracy; (2) visual field displacement produced an underestimation of the target distance only when the hand was not visible during the gesture and was always in the same direction displacement; and (3) the effect of the stationary structured visual field on aiming precision when the hand was not visible depended on the distance to the target. These results suggest that a stationary structured visual field is used to support the memory of the target position. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A theory of order relations in perceptual matching.

Relates order relations to research on retrieval processes and the representation of order information in memory. In 2 experimental tests, presentation of a study string of letters was followed by a test string to which the 6 undergraduate Ss responded "same" or "different." When adjacent letters were switched, RT was long and accuracy low, suggesting that a test letter is not simply compared to the letter in the same position in the study string; rather, the comparison is distributed across positions. The memory model assumes that the representation of a letter is distributed over position and that the comparison process assesses the amount of overlap between the test string and the memory representation. The diffusion retrieval model and overlap memory model are fitted to the data and goodness-of-fit is assessed. Shortcomings of alternative models are considered and applications of the model to related matching tasks, such as D. Taylor's (1976) converse of the perceptual matching task, and Angiolillo-Bent and L. Rips's (1981) multiple-element comparison task, are described. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual and memory search by process schizophrenics.

Compared the response times (RTs) of 20 process schizophrenics (10 paranoid and 10 nonparanoid) and 20 nonhospitalized controls (mean ages 39.2, 30.0, and 34.1 yrs, respectively) on a hybrid visual and memory search task in which Ss searched displays of up to 15 letters, reporting whether or not displays contained a target, which in different conditions was drawn from a memorized set of 1, 3, or 6 letters. RTs of all groups increased linearly with the product of the number in the memorized target set and the number of displayed letters. Although the intercepts and RTs of the schizophrenics (there were no paranoid–nonparanoid differences) exceeded those of controls, no group differences were found in slopes or in rates of increase in RT as a function of the number of memorized or displayed items. Results are interpreted in terms of a model proposed by W. Schneider and R. M. Shiffrin (1977), which indicates that process schizophrenics are retarded in processes associated with response production but not in a variety of processing stages involved in the comparison of displayed and memorized information. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A hemispheric division of labor aids mental rotation.

In the present study, we investigated whether a hemispheric division of labor is most advantageous to performance when lateralized inputs place unequal resource demands on the left and right cerebral hemispheres. In each trial, participants decided whether 2 rotated letters, presented either in the same visual field (within-field trials) or in opposite visual fields (across-field trials), were both of normal orientation, or whether one was normal and the other was mirror-reversed. To discriminate a letter's orientation, one must rotate the letter to the upright position. Therefore, we manipulated whether the two letters imposed similar or dissimilar demands on cognitive resources by varying the number of degrees that each letter needed to be rotated to reach the upright position. As predicted, in 2 experiments we found that the across-field advantage increased as the number of degrees each letter needed to be rotated became more dissimilar. These findings support a current model of hemispheric interactions, which posits that an unequal hemispheric distribution of cognitive load allows the cerebral hemispheres to take the lead for different aspects of cognitive processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Disruption to word or letter processing? The origins of case-mixing effects

MiXeD-cAsE stimuli have long been used to test whether word recognition is based on holistic visual information or preliminary letter identification. However, without knowing which properties of mixed-case stimuli disrupt processing, it is not possible to determine which visual units mediate word recognition. The present studies examined the effects of case mixing on word and nonword naming as a function of (a) whether spaces were inserted between letters and (b) whether letter size was alternated independent of letter case. The results suggest that case-mixing disruption effects are due to at least 2 factors: the introduction of inappropriate grouping between letters with the same size and case, and the disruption of transletter features. The data support a model of visual lexical access based on the input from multiple visually based units.