Unique physicochemical profile of beta-amyloid peptide variant Abeta1-40E22G protofibrils: conceivable neuropathogen in arctic mutant carriers.

A new early-onset form of Alzheimer's disease (AD) was described recently where a point mutation was discovered in codon 693 of the beta-amyloid (Abeta) precursor protein gene, the Arctic mutation. The mutation translates into a single amino acid substitution, glutamic acid-->glycine, in position 22 of the Abeta peptide. The mutation carriers have lower plasma levels of Abeta than normal, while in vitro studies show that Abeta1-40E22G protofibril formation is significantly enhanced. We have explored the nature of the Abeta1-40E22G peptide in more detail, in particular the protofibrils. Using size-exclusion chromatography (SEC) and circular dichroism spectroscopy (CD) kinetic and secondary structural characteristics were compared with other Abeta1-40 peptides and the Abeta12-28 fragment, all having single amino acid substitutions in position 22. We have found that Abeta1-40E22G protofibrils are a group of comparatively stabile beta-sheet-containing oligomers with a heterogeneous size distribution, ranging from >100 kDa to >3000 kDa. Small Abeta1-40E22G protofibrils are generated about 400 times faster than large ones. Salt promotes their formation, which significantly exceeds all the other peptides studied here, including the Dutch mutation Abeta1-40E22Q. Position 22 substitutions had significant effects on aggregation kinetics of Abeta1-40 and in Abeta12-28, although the qualitative aspects of the effects differed between the native peptide and the fragment, as no protofibrils were formed by the fragments. The rank order of protofibril formation of Abeta1-40 and its variants was the same as the rank order of the length of the nucleation/lag phase of the Abeta12-28 fragments, E22V>E22A?E22G>E22Q?E22, and correlated with the degree of hydrophobicity of the position 22 substituent. The molecular mass of peptide monomers and protofibrils were estimated better in SEC studies using linear rather than globular calibration standards. The characteristics of the Abeta1-40E22G suggest an important role for the peptide in the neuropathogenesis in the Arctic form of AD.

Concreteness and relational effects on recall of adjective-noun pairs.

Extending previous research on the problem, we studied the effects of concreteness and relatedness of adjective-noun pairs on free recall, cued recall, and memory integration. Two experiments varied the attributes in paired associates lists or sentences. Consistent with predictions from dual coding theory and prior results with noun-noun pairs, both experiments showed that the effects of concreteness were strong and independent of relatedness in free recall and cued recall. The generally positive effects of relatedness were absent in the case of free recall of sentences. The two attributes also had independent (additive) effects on integrative memory as measured by conditionalized free recall of pairs. Integration as measured by the increment from free to cued recall occurred consistently only when pairs were high in both concreteness and relatedness. Explanations focused on dual coding and relational-distinctiveness processing theories as well as task variables that affect integration measures.

Cognitive components of picture naming.

A substantial research literature documents the effects of diverse item attributes, task conditions, and participant characteristics on the case of picture naming. The authors review what the research has revealed about 3 generally accepted stages of naming a pictured object: object identification, name activation, and response generation. They also show that dual coding theory gives a coherent and plausible account of these findings without positing amodal conceptual representations, and they identify issues and methods that may further advance the understanding of picture naming and related cognitive tasks.

Psychology in Canada.

This chapter reviews how psychology in Canada evolved over half a century to become the most popular discipline in universities and a respected health-care and helping profession. The organization, journals, and funding of the scientific discipline are described. The importance of DO Hebb's research as the stimulus and foundation for discipline growth and significant research contributions to basic processes is identified. The multicultural mosaic of Canadian society and early research on second-language learning are shown to have influenced cross-cultural and social research. Canadian research contributions to basic processes and to the social and health sciences are reviewed. Although late to begin in Canada, clinical research and the profession of psychology are shown to have substantially developed over the past two decades. With large numbers of quality researchers and practitioners, psychology has a bright future in Canada.

Memory for pictures and sounds: independence of auditory and visual codes.

Three experiments examined the mnemonic independence of auditory and visual nonverbal stimuli in free recall. Stimulus lists consisted of (1) pictures, (2) the corresponding environmental sounds, or (3) picture-sound pairs. In Experiment 1, free recall was tested under three learning conditions: standard intentional, intentional with a rehearsal-inhibiting distracter task, or incidental with the distracter task. In all three groups, recall was best for the picture-sound items. In addition, recall for the picture-sound stimuli appeared to be additive relative to pictures or sounds alone when the distracter task was used. Experiment 2 included two additional groups: In one, two copies of the same picture were shown simultaneously; in the other, two different pictures of the same concept were shown. There was no difference in recall among any of the picture groups; in contrast, recall in the picture-sound condition was greater than recall in either single-modality condition. However, doubling the exposure time in a third experiment resulted in additively higher recall for repeated pictures with different exemplars than ones with identical exemplars. The results are discussed in terms of dual coding theory and alternative conceptions of the memory trace.

Referential processing: reciprocity and correlates of naming and imaging.

To shed light on the referential processes that underlie mental translation between representations of objects and words, we studied the reciprocity and determinants of naming and imaging reaction times (RT). Ninety-six subjects pressed a key when they had covertly named 248 pictures or imaged to their names. Mean naming and imagery RTs for each item were correlated with one another, and with properties of names, images, and their interconnections suggested by prior research and dual coding theory. Imagery RTs correlated .56 (df = 246) with manual naming RTs and .58 with voicekey naming RTs from prior studies. A factor analysis of the RTs and of 31 item characteristics revealed 7 dimensions. Imagery and naming RTs loaded on a common referential factor that included variables related to both directions of processing (e.g., missing names and missing images). Naming RTs also loaded on a nonverbal-to-verbal factor that included such variables as number of different names, whereas imagery RTs loaded on a verbal-to-nonverbal factor that included such variables as rated consistency of imagery. The other factors were verbal familiarity, verbal complexity, nonverbal familiarity, and nonverbal complexity. The findings confirm the reciprocity of imaging and naming, and their relation to constructs associated with distinct phases of referential processing.

Cognitive and motivational functions of imagery in human performance.

Anecdotal and research evidence suggest that imagery rehearsal can improve performance in a variety of sports activities at least some of the time. However, the reasons for the effects (or lack of them) are unclear. This paper proposes a conceptual framework that could be used to evaluate the available research literature and guide further research on the use of imagery techniques to modify performance. The framework is based on evidence that imagery mediates behaviour through either cognitive or motivational mechanisms, which affect specific or general response systems. Special emphasis is given to task analysis and the functions of memory and verbal mechanisms in imagery rehearsal.

Congruity and the perceptual comparison task.

The effects of congruity between comparatives and the relative magnitudes of to-be-compared stimuli were investigated in six perceptual comparison experiments. Experiments 1-5 failed to obtain congruity effects in purely perceptual tasks even when subjects had extensive practice with a relatively small stimulus set. Experiment 6 obtained a congruity effect with perceptual stimuli but only when the stimuli were described as representing real-world objects. All of the results indicated that congruity effects occur only in tasks that include major symbolic or memorial components; a review of the perceptual comparison literature reveals consistent support for this position. These findings are discussed in terms of expectancy and semantic coding interpretations of the congruity effect.

Symbolic comparisons of objects on color attributes.

Symbolic comparisons of object brightness and color were investigated in two experiments using words and outline drawings as stimuli. Both experiments yielded orderly symbolic distance effects. Contrary to prediction, no reliable picture advantages emerged. For color comparison, individual differences in word fluency and color memory predicted decision time with word stimuli. These results contrast sharply with those of previous comparison studies involving concrete dimensions. The results are discussed in terms of dual-coding theory and the role of verbal mechanisms in memory for object color.

Comparisons of mental clocks.

Subjects in three experiments were presented with pairs of clock times and were required to choose the one in which the hour and minute hand formed the smaller angle. In Experiments 1 and 2, the times were presented digitally, necessitating a transformation into symbolic representations from which the angular size difference could be inferred. The results revealed orderly symbolic distance effects so that comparison reaction time increased as the angular size difference decreased. Moreover, subjects generally reported using imagery to make the judgment, and subjects scoring high on test of imagery ability were faster than those scoring low on such tests. Experiment 3 added a direct perceptual condition in which subjects compared angles between pairs of hands on two drawn (analog) clocks, as well as a mixed condition involving one digital and one analog clock time. The results showed comparable distance effects for all conditions. In addition, reaction time increased from the perceptual, to the mixed, to the pure-digital condition. These results are consistent with predictions from an image-based dual-coding theory.

Memory for pictures and words as a function of level of processing: Depth or dual coding?

The experiment was designed to test differential predictions derived from dual-coding and depth-of-processing hypotheses. Subjects under incidental memory instructions free recalled a list of 36 test events, each presented twice. Within the list, an equal number of events were assigned to structural, phonemic, and semantic processing conditions. Separate groups of subjects were tested with a list of pictures, concrete words, or abstract words. Results indicated that retention of concrete words increased as a direct function of the processing-task variable (structural < phonemic

Free and serial recall of pictures, sounds, and words.

Pictures and sounds of familiar objects and their visual and auditory names were compared in free and serial recall tasks. The results of two experiments showed, most notably, that type of task interacted significantly with symbolic (verbal-nonverbal) and sensory (visual-auditory) modalities. Nonverbal items were remembered relatively better in free recall, whereas verbal items were superior in serial recall. In the visual modality, pictures were superior to words in both recall tasks; in the auditory modality, conversely, nonverbal sounds were inferior to words in serial recall but sounds and words did not differ in free recall. The results indicate that a satisfactory general theory of memory must encompass distinctions in both symbolic and sensory modalities as well as differences in the organizational demands of the memory task.

Perceptual comparisons through the mind's eye.

Four experiments tested a theory of memory and cognition which assumes that verbal and nonverbal information are processed in functionally distinct LTM systems. Subjects presented with pairs of pictures or printed names of animals and objects differing in rated real-life size were instructed to choose the conceptually larger member of each pair, the one that appeared to be farther away, or the one whose name was easier to pronounce. The following results were consistent with theoretical predictions: (1) RT to choose the larger member increased as the memory size difference decreased, for comparisons between as well as within conceptual categories; (2) memory size comparisons were faster with pictures than with words, whereas the reverse occurred for pronounceability comparisons; (3) with pictures, but not with words, size comparisons were significantly slower when real-life (memory) size relations conflicted with physical size relations than when the two were congruent; and (4) the size congruency effect was reversed for relative distance judgments of pictured pairs. These results cannot be easily explained by current verbal coding or abstract (propositional) theories of LTM representations.

The associative learning of the deaf: The effects of word imagery and signability.

In two experiments, deaf and hearing subjects learned paired associate lists in which rated visual imagery and signability (a measure of the ease with which a word can be represented as a gestural sign) were orthogonally varied. Visual presentation of three alternating study-recall trials resulted in significant positive effects of imagery for both deaf and hearing subjects, whereas signability facilitated recall only for deaf subjects. Examination of the relation between item attributes and reported learning strategy indicated that both deaf and hearing subjects used imaginal mediators more frequently for high-imagery than low-imagery pairs. A gestural sign strategy was reported almost exclusively by deaf subjects, particularly for high-signability pairs. These results suggest that an examination of the effects of sign language variables will contribute to an understanding of the qualitative differences in the associative learning of the deaf and hearing.

Pictures and words in visual search.

Ss in three experiments searched through an array of pictures or words for a target item that had been presented as a picture or a word. In Experiments I and II, the pictures were line drawings of familiar objects and the words were their printed labels; in Experiment III, the stimuli were photographs of the faces of famous people and their corresponding printed names. Search times in Experiments I and II were consistently faster when the array items were pictures than when they were words, regardless of the mode of the target items. Search was also faster with pictures than with words as targets when the search array also consisted of pictures, but target mode had no consistent effect with words as array items. Experiment III yielded a completely different pattern of results: Search time with names as targets and faces as search array items was significantly slower than in the other three conditions, which did not differ from each other. Considered in relation to several theories, the results are most consistent with a dual-coding interpretation. That is, items that are cognitively represented both verbally and as nonverbal images can be searched and compared in either mode, depending on the demands of the task. The mode actually used depends on whether the search must be conducted through an array of pictures or words.