Flexibility in scanning described images

Two experiments investigated why past research has shown that described images lead to the typical increase in reaction time (RT) with increasing memory set size (m), but undescribed images do not. Experiment 1 used ms 6 through 8. A described image group showed a linear relation between m and RT up to a m of 6, and no increase in RT thereafter. A story group (which was asked to tell a brief story for words in a memory set) and a repetition group showed a linear relation between m and RT throughout the range of ms, whereas an image group showed no relation between m and RT. Experiment 2 essentially replicated the first experiment but manipulated memory strategy as a within subject variable. Similar results were found. The apparent change from "serial" to "parallel" processing by the described image groups in both studies reinforces the notion of flexibility in processing, particularly when multiple representations are formed or when multiple encoding strategies are used.     

Memory scanning for words in visual images

This study attempts to replicate an experiment reported by Seamon (1972). In the present investigation, as in the study by Seamon, the scanning of short-term memory was compared when its contents were rehearsed words vs. a mental image. Memory sets were composed of either one, two, or three words. In the relational imagery group, subjects were required to form a single interactive mental scene of the entities which the memory set words represent. Nonimagery subjects were given instructions to covertly rehearse the memory set. In both groups, the usual memory set size (m) effect was obtained, i.e., reaction time (RT) increased linearly with m. Moreover, the set size effect was the same for both groups. This latter finding stands in marked contrast to the result obtained by Seamon; he found no effect of set size when subjects were given interactive imagery instructions. Because of the failure to replicate Seamon, an additional group of subjects were given imagery instructions. For this latter group, some of the procedural discrepancies between the relational imagery group of the present study and the corresponding group in Seamon’s study were resolved. Also, in this additional group, the set size effect was examined as a function of the subjects’ ratings of the quality of the images which they had formed. The same set size effect was found for this additional group, and the effect was independent of image quality.     

Implicit and explicit memory for odors: Hemispheric differences

In two experiments, implicit and explicit tests were used to investigate the lateralization of odor memory. Odors were at all times presented monorhinically. At test, odors were presented to either the ipsi- or the contralateral side of the nostril used for inspection. In Experiment 1, participants were first primed to a set of odors. At test, response latencies for odor identification were measured. The results were that priming odors tested via the left but not the right nostril were identified faster than control odors. In Experiment 2, a similar design probed episodic recognition memory. Memory performance did not differ between the left and right nostrils, but the measures of response latency favored the right side. The study demonstrates that it is possible to tap differences in memory performance between the cerebral hemispheres through monorhinic presentation of odors in healthy persons, and that these differences depend on the test nostril rather than the inspection nostril.     

EEG correlates of sustained attention: Hemispheric and sex differences

Subjects were presented with sets of four digits, and had to respond only when all the digits in a set were odd. The EEG was measured from occipital-parietal derivations over the left and right hemispheres, and the energy within each of five frequency bands was integrated over 3-sec epochs corresponding to the presentation of individual sets of digits. The EEG abundance was found to be lower the more a digit set resembled a signal, but hemisphere differences in this effect tended to be small and to occur only in certain frequency bands. The effect for stimulus type changed over time in some frequency bands, but there were no differences between the hemispheres in this change. Nor were sex differences in lateralization found. Reaction time was found to correlate positively with (a) EEG abundance, and (b) EEG differentiation of stimuli, in the theta and low alpha frequency bands.     

Perceptual and conceptual organization of facial emotions: Hemispheric differences

Patients with lesions to either the right or left hemisphere and control subjects were asked to judge the similarity of pairs of photographs of a person displaying different emotions, and of pairs of emotion words. The results were submitted to a multidimensional scaling analysis. Right-hemisphere-damaged subjects were found to be more impaired at perceiving facial emotions than were left-hemisphere-damaged subjects or controls, and this impairment was not confined to the perception of a subset of facial emotions nor to judging emotional valence (Pleasantness versus Unpleasantness). Rather, subtle impairments in perceiving a wide range of facial emotions were found, mostly concerning differentiation of the Positive-Negative and Attention-Rejection dimensions, and concerning the strategies the subjects used to make their judgments. The right-hemisphere-damaged subjects performed comparably to controls in their ratings of emotion words, suggesting that their ability to conceptualize emotional states was intact and that their impairment was strictly in the perception of emotion.     

Hemispheric differences for orthographic and phonological processing

The role of hemispheric differences for the encoding of words was assessed by requiring subjects to match tachistoscopically presented word pairs on the basis of their rhyming or visual similarity. The interference between a word pair's orthography and phonology produced matching errors which were differentially affected by the visual field/hemisphere of projection and sex of subject. In general, right visual field/left hemisphere presentations yielded fewer errors when word pairs shared similar phonology under rhyme matching and similar orthography under visual matching. Left visual field/right hemisphere presentations yielded fewer errors when word pairs were phonologically dissimilar under rhyme matching and orthographically dissimilar under visual matching. Males made more errors and demonstrated substantially stronger hemispheric effects than females. These patterns suggested visual field/hemispheric differences for orthographic and phonological encoding occurred during the initial stages of word processing and were more pronounced for male compared to female subjects.     

Hemispheric differences in processing emotions and faces.

Visual field differences for the recognition of emotional expression were investigated using a tachistoscopic procedure. Cartoon line drawings of five adult male characters, each with five emotional expressions ranging from extremely positive to extremely negative, were used as stimuli. Single stimuli were presented unilaterally for 85 msec. Subjects (N = 20) were asked to compare this target face to a subsequent centrally presented face and to decide whether the emotional expressions of the two faces, or the character represented by the two faces, were the same or different. Significant left visual field (LVF) superiorities for both character and emotional expression recognition were found. Subsequent analyses demonstrated the independence of these effects. The LVF superiority for emotional judgments was related to the degree of affective expression, but that for character recognition was not. The results of this experiment are consistent with experimental and clinical literature which has indicated a right hemispheric superiority for face recognition and for processing emotional stimuli. The asymmetry for emotion recognition is interpreted as being an expression of the right hemisphere's synthetic and integrative characteristics, its holistic nature, and its use of imagic associations.     

Memory scanning by children: Meaningfulness and mediation

Two experiments were performed for the purpose of isolating factors that influence speed of memory scanning by children. The first experiment revealed an interaction involving age and type of stimulus. Young children required relatively greater time to process ambiguous stimuli. The second experiment, involving a pretraining phase designed to induce mediation, showed that preschool children scan representations more rapidly when given instructions to apply a mediator.     

Categorization versus distance: Hemispheric differences for processing spatial information

It has been hypothesized that the brain computes two different kinds of spatial-relation representations: one used to assign a spatial relation to a category and the other used to specify metric distance with precision. The present visual half-field experiment offers support for this distinction by showing that the left and right cerebral hemispheres make more effective use of the categorization and metric distance representations, respectively. Furthermore, the inclusion of a bilateral stimulus presentation condition permits the computation of a reversed association that offers additional support for the distinction between two types of spatial-relation representation.     

Hemispheric sensitivity differences in the perception of colour

Signal detection analysis was performed on data obtained from discrimination tasks using lateralized coloured stimuli. It was found that there was a right hemisphere superiority in discriminability to both hue and saturation.     

Hemispheric differences in the voluntary inhibition of movement

Twenty normal, twenty left-, and fifteen right-brain injured subjects, all right-handed, were assigned a sequence of voluntary inhibition of 23 movements. The inhibition lapse was recorded. Statistical analyses indicated a high performance in the normal and a deficient performance in left-brain injured subjects, no influence of the neurological symptoms on groups' achievement, a handicap in the subjects affected by a frontal lesion in the right brain, a hierarchical clustering of items varying according to the groups, and an organ-group interaction.     

Memory for moving and static images

Despite the substantial interest in memory for complex pictorial stimuli, there has been virtually no research comparing memory for static scenes with that for their moving counterparts. We report that both monochrome and color moving images are better remembered than static versions of the same stimuli at retention intervals up to one month. When participants studied a sequence of still images, recognition performance was the same as that for single static images. These results are discussed within a theoretical framework which draws upon previous studies of scene memory, face recognition, and representational momentum.     

Hemispheric interaction,task complexity,and emotional valence: Evidence from naturalistic images

Two experiments extend the ecological validity of tests of hemispheric interaction in three novel ways. First, we present a broad class of naturalistic stimuli that have not yet been used in tests of hemispheric interaction. Second, we test whether probable differences in complexity within the class of stimuli are supported by outcomes from measures of hemispheric interaction. Third, we use a procedure that presents target stimuli at fixation rather than at a lateralized location in order to more closely approximate normal viewing behavior.     

Hemispheric differences in visual search of simple line arrays

Summary The effects of perceptual organization on hemispheric visual-information processing were assessed with stimulus arrays composed of short lines arranged in columns. A visual-search task was employed in which subjects judged whether all the lines were vertical (same) or whether a single horizontal line was present (different). Stimulus-display organization was manipulated in two experiments by variation of line density, linear organization, and array size. In general, left-visual-field/right-hemisphere presentations demonstrated more rapid and accurate responses when the display was perceived as a whole. Right-visual-field/left-hemisphere superiorities were observed when the display organization coerced assessment of individual array elements because the physical qualities of the stimulus did not effect a gestalt whole. Response times increased somewhat with increases in array size, although these effects interacted with other stimulus variables. Error rates tended to follow the reaction-time patterns. The results suggest that laterality differences in visual search are governed by stimulus properties which contribute to, or inhibit, the perception of a display as a gestalt. The implications of these findings for theoretical interpretations of hemispheric specialization are discussed.     

Hemispheric differences for semantically and phonologically primed nouns: A tachistoscopic study in normals

Normal individuals performed two matching tasks. In one task, semantic processing, synonyms had to be recognized. Half the stimuli were picturable and half were nonpicturable nouns. In this task, recognition of picturable synonyms was found to have hemifield symmetry, whereas recognition of nonpicturable synonyms yielded a left-hemisphere superiority, indicating that semantic matching itself did not reveal equal performance of both hemispheres. It is concluded that picturable synonyms might be recognized either by processes of visual imagery, which pertain to right-hemisphere function, or by their phonological or phonic features, which are processed by the left hemisphere. The other task, shown in previous research to exhibit a left-hemisphere superiority, was to decide if two nouns (homophones) were equally pronounced. Here a distinct left-hemisphere advantage was revealed.     

Hemispheric differences in the interference among components of compound gratings

The relationship between local/global and high/low spatial-frequency processing in hemispheric asymmetries was explored. Subjects were required to judge the orientation of a high- or low-spatial-frequency component of a compound grating presented in the left visual field (LVF) or right visual field (RVF). In Experiment 1, attention was focused on one or the other component. A signal detection analysis indicated that sensitivity (d′) to the high-spatial-frequency target was reduced more by the presence of the low-spatial-frequency component when both were presented in the LVF rather than in the RVF. In Experiment 2, subjects determined whether a target orientation was present, independent of spatial frequency at only a single level (i.e., at the high- or low-spatial-frequency level), as opposed to both or neither level. An RVF/LH (left hemisphere) advantage was found when the decision was based on the orientation of the high-frequency component. The asymmetrical influence of visual field of presentation and spatial frequency upon sensitivity is discussed in terms of hemispheric differences in the magnitude of inhibition between spatial-frequency channels and in the role of transient channel activity to capture and direct higher order attentional processes.     

Hemispheric differences in the effects of context on vowel perception

Listeners perceive speech sounds relative to context. Contextual influences might differ over hemispheres if different types of auditory processing are lateralized. Hemispheric differences in contextual influences on vowel perception were investigated by presenting speech targets and both speech and non-speech contexts to listeners’ right or left ears (contexts and targets either to the same or to opposite ears). Listeners performed a discrimination task. Vowel perception was influenced by acoustic properties of the context signals. The strength of this influence depended on laterality of target presentation, and on the speech/non-speech status of the context signal. We conclude that contrastive contextual influences on vowel perception are stronger when targets are processed predominately by the right hemisphere. In the left hemisphere, contrastive effects are smaller and largely restricted to speech contexts.