Gaze direction affects visuo-spatial short-term memory

Hemispheric asymmetries were investigated by changing the horizontal position of stimuli that had to be remembered in a visuo-spatial short-term memory task. Observers looked at matrices containing a variable number of filled squares on the left or right side of the screen center. At stimulus offset, participants reproduced the positions of the filled squares in an empty response matrix. Stimulus and response matrices were presented in the same quadrant. We observed that memory performance was better when the matrices were shown on the left side of the screen. We distinguished between recall strategies that relied on visual or non-visual (verbal) cues and found that the effect of gaze position occurred more reliably in participants using visual recall strategies. Overall, the results show that there is a solid enhancement of visuo-spatial short-term memory when observers look to the left. In contrast, vertical position had no influence on performance. We suggest that unilateral gaze to the left activates centers in the right hemisphere contributing to visuo-spatial memory.     

Asymmetric interference between domains: evidence from the stimulus order effect in complex span tasks

The stimulus order effect refers to the finding that recall in complex span tasks is better when span lists begin with a longer processing task and end with a shorter task than when these processing tasks are presented in the reverse order. This study independently manipulated processing time and processing difficulty between Long-final and Short-final lists. The processing task required participants to solve arithmetic problems with either verbal (Experiment 1) or visuospatial (Experiment 2) materials. The memory items used in the storage task were either digits (verbal material) or dots-in-matrices (visuospatial materials). Storage of both verbal and visuospatial materials was sensitive to the change in processing difficulty, but not processing time. Furthermore, this study provides further evidence for the asymmetry of domain interference in working memory. The similarities and differences between verbal and visuospatial storage in working memory are discussed.     

Verbal coding and the storage of form-position associations in visual-spatial short-term memory

Short-term memory for form-position associations was assessed using an object relocation task. Participants attempted to remember the positions of either three or five Japanese Kanji characters, presented on a computer monitor. Following a short blank interval, participants were presented with 2 alternative Kanji, only 1 of which was present in the initial stimulus, and the set of locations occupied in the initial stimulus. They attempted to select the correct item and relocate it back to its original position. The proportion of correct item selections showed effects of both articulatory suppression and memory load. In contrast, the conditional probability of location given a correct item selection showed an effect of load but no effect of suppression. These results are consistent with the proposal that access to visual memory is aided by verbal recoding, but that there is no verbal contribution to memory for the association between form and position.     

Perceptual and conceptual training mediate the verbal overshadowing effect in an unfamiliar domain

Describing memory for a nonverbal perceptual stimulus can impair recognition. This verbal overshadowing effect may occur when perceptual expertise exceeds verbal expertise, but previous evidence for this hypothesis has been strictly correlational. We conducted two experiments, exploring the relation between expertise and verbal overshadowing by manipulating perceptual and conceptual knowledge. Participants received perceptual training (categorizing mushrooms), conceptual training (lecture), or no training, then viewed a mushroom and described it or not. A recognition test followed. In Experiment 1, perceptual training increased susceptibility to verbalization relative to the no training condition. However, conceptual training did not insulate individuals from the verbal overshadowing effect. Experiment 2 was modified to enhance both forms of training. It replicated the finding that perceptual training increases vulnerability to verbal overshadowing, and indicated that, when sufficiently emphasized, verbalization may be useful following conceptual training. The results demonstrate the role that different forms of learning and expertise may play in mediating language influences on recognition memory.     

Hemispheric alpha asymmetries of words with positive, negative, and neutral arousal values preceding tasks of recall and recognition: Electrophysiological and behavioral results from stuttering males and nonstuttering males and females

Hemispheric alpha asymmetries were obtained for stuttering males and nonstuttering males and females for words of positive, negative, and neutral arousal values. Electroencephalographic data were gathered during the presentations of stimulus words and during the actual nonoral recall and recognition of the stimulus items. Stuttering males demonstrated right-hemispheric alpha suppression across stimulus words and tasks as contrasted with left-hemispheric alpha suppression for the nonstuttering males and females. Stuttering males were also shown to recall and recognize fewer words than the nonstuttering subjects across arousal categories. Subjects were also administered a modified version of A. Paivio's (1971, In B. Randhawa & W. Coffman, Eds., Visual thinking, learning, and communication, New York: Academic Press) Individual Differences Questionnaire (IDQ). Results showed our stuttering males to have obtained lower scores on the verbal and imagery questions of the IDQ as compared to the nonstuttering groups. Hemispheric alpha asymmetry results and memory performance from the stuttering males are discussed relative to nonsegmental, right-hemispheric processing strategies.     

Verbal, visual, and spatial working memory in written language production

College students wrote definitions of either abstract or concrete nouns in longhand while performing a concurrent working memory (WM) task. They detected either a verbal (syllable), visual (shape), or spatial (location) stimulus and decided whether it matched the last one presented 15-45s earlier. Writing definitions of both noun types elevated the response time to verbal targets above baseline. Such interference was observed for visual targets only when defining concrete nouns and was eliminated entirely with spatial targets. The interference effect for verbal targets was the same whether they were read or heard, implicating phonological storage. The findings suggest that language production requires phonological or verbal WM. Visual WM is selectively engaged when imaging the referents of concrete nouns.     

Hemispheric differences in stimulus identification

Subjects were presented with either verbal (letters) or nonverbal (outline forms) stimuli to their left or right cerebral hemispheres. Verbal items presented with a lateral masking stimulus were identified more quickly and accurately when presented to the right hemisphere rather than to the left. When the letters were presented without a masking stimulus, weak hemispheric effects were obtained. Nonverbal forms demonstrated faster reaction time and fewer errors for right-hemisphere presentations under both masked and unmasked conditions. Retinal locus of the display item was also varied and produced faster responding with fewer errors when the stimulus was presented foveally rather than peripherally under all display conditions. These effects were attributed to the use of a manual response procedure that effectively reduced the ability of subjects to employ names for the stimulus objects.     

Performance dissociation during verbal and spatial working memory tasks

Past research has inconsistently distinguished the neural substrates of various types of working memory. Task design and individual performance differences are known to alter patterns of brain response during working-memory tasks. These task and individual differences may have produced discrepancies in imaging findings. This study of 50 healthy adults (M(age) = 19.6 yr., SD = .8) examined performance during various parametric manipulations of a verbal and spatial n-back working-memory task. Performance systematically dissociated on the basis of working-memory load, working memory type, and stimulus difficulty, with participants having greater accuracy but slower response time during conditions requiring verbal versus spatial working memory. These findings hold implications for cognitive and neuroimaging studies of verbal and spatial working memory and highlight the importance of considering both task design and individual behavior.     

Ethanol reduces rCFB activation of left dorsolateral prefrontal cortex during a verbal fluency task

In a previous study in normal subjects (Wendt et al., 1994), using a reversing checkerboard as activation stimulus, we found that the coupling between local neuronal activity and regional cerebral blood flow was preserved following ethanol, and that a right-sided occipital activation response seen during sobriety became symmetrical during inebriation. In the present study we investigated if ethanol has a detrimental effect also on the activation of the left dorsolateral prefrontal cortex found in normals during verbal fluency. Measurements of regional cerebral blood flow in 20 healthy, young, male, right-handed volunteers during rest and verbal fluency were made during sobriety and inebriation (0.06% blood alcohol concentration) with a 1-week interval. We found a decrease in word production during inebriation. The normal activation within the frontotemporal part of the left dorsolateral prefrontal cortext was preserved during inebriation. The activation of this region seems thus to be robust to the effects of ethanol. During inebriation no activation response to the word fluency test was found in the anterior prefrontal part of the dorsolateral prefrontal cortex. This region is important for working, temporal, and short-term memory functions, processes that are affected by ethanol. Hemispheric functioning and specialization seem to be adversely affected by ethanol, regardless of which hemisphere is most involved while sober.     

Validating age-related functional imaging changes in verbal working memory with acute stroke

Functional imaging studies consistently find that older adults recruit bilateral brain regions in cognitive tasks that are strongly lateralized in younger adults, a characterization known as the Hemispheric Asymmetry Reduction in Older Adults model. While functional imaging displays what brain areas are active during tasks, it cannot demonstrate what brain regions are necessary for task performance. We used behavioral data from acute stroke patients to test the hypothesis that older adults need both hemispheres for a verbal working memory task that is predominantly left-lateralized in younger adults. Right-handed younger (age ? 50, n = 7) and older adults (age > 50, n =21) with acute unilateral stroke, as well as younger (n =6) and older (n =13) transient ischemic attack (TIA) patients, performed a self-paced verbal item-recognition task. Older patients with stroke to either hemisphere had a higher frequency of deficits in the verbal working memory task compared to older TIA patients. Additionally, the deficits in older stroke patients were mainly in retrieval time while the deficits in younger stroke patients were mainly in accuracy. These data suggest that bihemispheric activity is necessary for older adults to successfully perform a verbal working memory task.     

Unhindered Spatial Processing During Route Memorization is Required to Maximize Both Spatial and Verbal Route Knowledge

To successfully remember a route in a physical environment, individuals are believed to process and store both verbal and spatial information of that route. The present study tested whether both spatial and verbal contents are necessary to form an effective route memory. For that purpose, route learning was performed in three concurrent task conditions (spatial, verbal and control) and appraised at two moments in time, via three route memory tests (spatial, verbal and spatial–verbal). Results showed that route memory generally improved across time and that spatial information was remembered better than verbal information. The concurrent spatial condition resulted in lower retention scores of both spatial and verbal route knowledge. These results suggest that effective spatial processing forms a scaffold without which long‐term retention lacks detail of both spatial and verbal route knowledge. It is discussed how these findings add to understanding spatial memory of routes. Copyright © 2013 John Wiley & Sons, Ltd.     

Coding of stimuli by animals: Retrospection, prospection, episodic memory and future planning

When animals code stimuli for later retrieval they can either code them in terms of the stimulus presented (as a retrospective memory) or in terms of the response or outcome anticipated (as a prospective memory). Although retrospective memory is typically assumed (as in the form of a memory trace), evidence of prospective coding has been found when response intentions and outcomes are particularly salient. At a more abstract level is the question of whether animals are able figuratively to travel back in time to recover memories of past events (episodic memory) and forward in time to predict future events (future planning). Although what would constitute adequate evidence of episodic memory and future planning is controversial, preliminary evidence suggests that animals may be capable of both forms of subjective time travel.     

The influence of working memory load on the Simon effect

The contribution of spatial and verbal working memory (WM) to the processing of stimulus location in the Simon task was examined in two experiments. Subjects performed the Simon task in single- and dual-task conditions. In the dual-task conditions, individuals first encoded the locations of four boxes/pseudocharacters or the identity of seven characters in memory, then responded to the color of a Simon stimulus, and finally received a test for the WM set. The Simon effect was insensitive to spatial WM load and was abolished by verbal WM load. These data reveal a role of verbal WM in the processing of spatial location in the Simon task. In addition, the data are inconsistent with dual-route models of the Simon effect and may support response discrimination accounts of the mechanisms underlying the processing of spatial location in the Simon task.     

Hemispheric asymmetries in the time course of recognition memory

Hemispheric specialization has been studied extensively within subfields ranging from perception to language comprehension. However, the study of asymmetries for basic memory functions—an area that holds promise for bridging these low- and high-level cognitive domains—has been sporadic at best. We examined each hemisphere’s tendency to retain verbal information over time, using a continuous recognition memory task with lateralized study items and central test probes. We found that the ubiquitous advantage of the left hemisphere for the processing and retention of verbal information is attenuated and perhaps even reversed over long retention intervals. This result is consistent with theories that propose differences in the degree to which the hemispheres maintain veridical versus semantically transformed representations of the input they receive.     

Cross-modal priming and explicit memory in patients with verbal production deficits

Implicit memory is often thought to reflect an influence of past experience on perceptual processes, yet priming effects are found when the perceptual format of stimuli changes between study and test episodes. Such cross-modal priming effects have been hypothesized to depend upon stimulus recoding processes whereby a stimulus presented in one modality is converted to other perceptual formats. The present research examined recoding accounts of cross-modal priming by testing patients with verbal production deficits that presumably impair the conversion of visual words into auditory/phonological forms. The patients showed normal priming in a visual stem completion task following visual study (Experiment 1), but showed impairments following auditory study in both implicit (Experiment 2) and explicit (Experiment 3) stem completion. The results are consistent with the hypothesis that verbal production processes contribute to the recoding of visual stimuli and support cross-modal priming. The results also indicate that shared processes contribute to both explicit memory and cross-modal implicit memory.     

Short-term forgetting without interference

In the 1st reported experiment, we demonstrate that auditory memory is robust over extended retention intervals (RIs) when listeners compare the timbre of complex tones, even when active or verbal rehearsal is difficult or impossible. Thus, our tones have an abstract timbre that resists verbal labeling, they differ across trials so that no "standard" comparison stimulus is built up, and the spectral change to be discriminated is very slight and therefore does not shift stimuli across verbal categories. Nonetheless, performance in this nonverbal immediate memory task was better at short (1-, 2-, or 4-s) than long (8-, 16-, or 32-s) RIs, an outcome predicted by temporal distinctiveness theory whereby at long RIs, tones are closer in time to tones on previous trials. We reject this account in the 2nd experiment, where we demonstrate that the ratio of RI to intertrial interval makes absolutely no difference to performance. We suggest that steady forgetting is consistent with a psychoacoustically derived conception of an auditory memory (the timbre memory model) that embodies time-based forgetting in the absence of feature-specific interference.     

Flexibility of working memory encoding in a sentence–picture–sound verification task

Dual-process accounts of working memory have suggested distinct encoding processes for verbal and visual information in working memory, but encoding for nonspeech sounds (e.g., tones) is not well understood. This experiment modified the sentence–picture verification task to include nonspeech sounds with a complete factorial examination of all possible stimulus pairings. Participants studied simple stimuli–pictures, sentences, or sounds–and encoded the stimuli verbally, as visual images, or as auditory images. Participants then compared their encoded representations to verification stimuli–again pictures, sentences, or sounds–in a two-choice reaction time task. With some caveats, the encoding strategy appeared to be as important or more important than the external format of the initial stimulus in determining the speed of verification decisions. Findings suggested that: (1) auditory imagery may be distinct from verbal and visuospatial processing in working memory; (2) visual perception but not visual imagery may automatically activate concurrent verbal codes; and (3) the effects of hearing a sound may linger for some time despite recoding in working memory. We discuss the role of auditory imagery in dual-process theories of working memory.     

Developmental recall lag in learning-disabled children: Perceptual deficit or verbal mediation deficiency?

To investigate the development of mediational deficiencies in verbal and non-verbal visual short-term memory of learning disabled children, the recall task of Atkinson, Hansen, and Bernback was administered to learning disabled children in two experimental conditions. In Experiment 1 no significant diferences on nonverbal short-term memory recall between normal and learning-disabled children were found. Similar recall responses (e.g., middle response bias, primacy effects, and recency effects) were found for both groups. Non-verbal recall was comparable for disabled and normal children as suggested by stimulus content and association scores/. Experiment 2 found that while the effects of overt rehearsal on pretrained labels on learning disabled children's recall was negligible, labels provided superior recall for normal children. Results suggested that learning disabled children suffer from a verbal mediational deficiency consistent with Flavell's (1970) mediation deficiency hypothesis.The research herein was supported by a faculty research grant at the University of Northern Colorado. Appreciation is due to the Albuquerque (New Mexico) Public School System and the Richland 1 School District, Columbia, South Carolina.     

Effects of concurrent verbal memory on recognition of stimuli from the left and right visual fields.

Two experiments examined the effect of concurrently holding 0, 2, 4, or 6 nouns in memory on the recognition of visual stimuli briefly presented to the left or right visual fields. When stimuli to be visually recognized were complex visuospatial forms it was found that a relatively easy memroy load of 2 or 4 nouns improved visual recognition accuracy on right visual field (left-hemisphere) trials relative to the no-memory condition; however, a more difficult memory load of 6 nouns decreased visual recognition accuracy to a level slightly below the no-memory condition. There were no effects of concurrent verbal memroy on visual form recognition on left visual field (right-hemisphere) trials. When the stimuli to be visually recognized were words it was found that a relatively easy memroy load of 2 or 4 nouns improved visual recognition accuracy and a more difficult load of 6 nouns decreased visual recognition accuracy on both left and right visual field trials. The complete pattern of results indicates that several factors including cerebral hemisphere specialization, stimulus codability, selective perceptual orientation, and selective cerebral hemisphere interference interact in systematic ways to produce overall visual laterality effects.