The processing of hierarchical stimuli: effects of retinal locus, locational uncertainty, and stimulus identity.
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Adult↗
Biomedical subjects
M R Lamb
Publications and source records attributed to M R Lamb.
Effects of lesions of temporal-parietal junction on perceptual and attentional processing in humans.
When stimuli with larger forms (global) containing smaller forms (local) are presented to subjects with large lesions in the right hemisphere, they are more likely to miss the global form than the local form, whereas subjects with large lesions in the left are more likely to miss the local than the global form. The present study tested whether the global/local impairment in subjects with posterior lesions was due to deficits in controlled attentional processes, passive perceptual processes, or both. Attentional control was examined by measuring reaction time changes when the probability of a target appearing at either the global or local level was varied. Patients with unilateral right or left lesions centered in temporal-parietal regions and age-matched controls served as subjects. Because neurophysiological and neuropsychological evidence have implicated temporal regions in visual discrimination and inferior parietal regions in the allocation of attention to locations in the visual field, patients with left hemisphere lesions were further subdivided into those with lesions centered in the superior temporal gyrus (LSTG) or rostral inferior parietal lobule (LIPL). Patients with right hemisphere injury could not be analogously subdivided. The results revealed that the LSTG group was able to control the allocation of attention to global and local levels normally, while the LIPL group was not. In contrast, the LSTG group showed a strong baseline reaction time advantage toward global targets, while normals and the LIPL group showed no advantage toward one level or the other. Finally, the perceptual component was affected differentially by lesions in the right hemisphere and LSTG, with lesions in the left favoring global targets and lesions in the right favoring local targets. These findings indicate that the hemispheric global/local asymmetry is due to a perceptual mechanism with a critical anatomical locus centered in the STG.
Adult↗
Selective attention: effects of cuing on the processing of different types of compound stimuli.
Pigeons in a matching-to-sample experiment received (a) element samples (one of two colors or vertical or horizontal white lines), (b) separated compound samples (a color and a line element presented together), and (c) unified compound samples (vertical or horizontal colored lines). In Phase I, test stimuli were the two elements from one dimension; the dimension tested varied randomly when the sample was a compound. Element samples were matched better than unified samples, which were matched better than separated samples. In Phase II, two samples preceded the tests. On EC trials, the first sample (S1) was an element, and the second sample (S2) was a compound; on CE trials this order was reversed. One element of the compound sample was always the one appearing as the element sample on that trial (e.g., S1 = red, S2 = red-vertical). This element also served as the correct test alternative (e.g., test = red+ vs. green) except on probe trials when the correct test was the other element appearing in the compound (e.g., test = vertical+ vs. horizontal). Accuracy varied as a function of sample sequence when the compound was separated (EC greater than CE on nonprobe trials and CE greater than EC on prove trials). This pattern was not observed when the compound was unified. The data suggest that the element in EC trials served as a cue that increased processing of the cued dimension and decreased processing of the noncued dimension of separated compounds. However, both dimensions of unified compounds seem to have been processed regardless of cuing.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Effect of acute alcohol on attention and the processing of hierarchical patterns.
Subjects received 100-msec exposures of hierarchical patterns consisting of a large "global" letter composed of several smaller "local" letters. Subjects were to respond whether a target letter was present at the global or at the local level. In the Neutral Bias condition target letters occurred randomly and equally often at the global and local levels. In the Global Bias condition, 79% of the targets occurred at the global and 21% at the local level. In the Local Bias condition, 79% of the targets occurred at the local and 21% at the global level. Subjects indicated by pressing a key which of two target letters had appeared on that trial. Subjects received either a placebo drink, a drink containing 0.7 ml of Alcohol per kg body weight, or a drink containing 1 ml of Alcohol per kg body weight. Placebo subjects were better at detecting letters at the global than at the local level in the Global Bias condition, better at local than global in the Local Bias condition, and about equally good at both levels in the Neutral Bias condition. Alcohol had no effect on detection of letters at the local level in any of the bias conditions but reduced detection of letters at the global level except when subjects were biased globally. The data suggest that alcohol does not affect attentional capacity. Instead, alcohol seems to affect either how attentional capacity is allocated or the global processing mechanism itself.
Adult↗
Effects of morphine, ethylketocyclazocine, and N-allylnormetazocine on classical conditioning of the rabbit nictitating membrane response.
The rabbit's nictitating membrane response was classically conditioned to tone and light conditioned stimuli presented for 800 ms before delivery of a 100-ms unconditioned shock stimulus. Both the mu receptor agonist morphine (5 mg/kg) and the kappa receptor agonist ethylketocyclazocine (1 mg/kg) significantly retarded the acquisition of conditioned responses (CRs). The retardant effects of both morphine and ethylketocyclazocine on CR acquisition could still be detected when the rabbits were tested 5 days after cessation of drug injections. At the dose employed in this study (5 mg/kg), the sigma receptor agonist N-allylnormetazocine had no effect on acquisition. The retardant effects of morphine and ethylketocyclazocine on acquisition were significantly antagonized by both naloxone (1 mg/kg) and N-allylnormetazocine (5 mg/kg). It was suggested that mu and possibly kappa receptors are involved in the retardant effects of opiates on the acquisition of classically conditioned responses.
Animals↗
Functional domains in introns. RNA processing intermediates in cis- and trans-acting mutants in the penultimate intron of the mitochondrial gene for cytochrome b.
The penultimate intron of the split mitochondrial gene (cob) for apocytochrome b of Saccharomyces cerevisiae is of particular interest; it contains a long unassigned reading frame, is present in both long form (six exons) and short form (three exons) of the gene, and a product expressed from it is required for the removal of its transcript and that of an intron in the transcript of the oxi3 gene. Complementation analysis shows mutants in this intron to be either cis-dominant or transrecessive. Cis-dominant mutants are located in the first third (approximately 350 base pairs) of the open and near the 3'-end of the closed reading frame, while trans-recessive mutants are scattered throughout the remaining two-thirds (approximately 750 base pairs) of the open frame. Mutants in both classes exhibit the same pattern of splicing defects in their transcripts, but for different reasons. Those in the trans-recessive class lack a functional maturase (probably a protein of Mr = 27,000) encoded wholly within the 3'-terminal segment of the intron, and for this reason also fail to express oxi3. In contrast, cis-dominant mutants are incapable of providing the splicing complex with a substrate of appropriate 2 degrees structure. They also accumulate a novel transcript, 1900 nucleotides long, which contains the intron fused to the downstream (3') exons. This may reflect an inability of the splicing complex to complete the normal sequence of cleavage of the intron at its downstream junction and the ligation of the two exonic moieties.
Base Composition↗
Evidence for translated intervening sequences in the mitochondrial genome of Saccharomyces cerevisiae.
In yeast, the mitochondrial genes for subunit I of cytochrome oxidase (oxi3) and for apocytochrome b (cob) are known to be split. In some strains, the latter contains five intervening sequences, three of which coincide with clusters of mutational sites referred to in their order of transcription as the loci box3, 10, and 7, respectively. Mutations at the first of these result in the accumulation of novel, large polypeptides (apparent Mr congruent to 43,000) believed to originate from a fusion of sequences found in the NH2-terminal segment of apocytochrome b to others encoded in the intervening sequence itself. We now provide evidence for close similarities of at least a part of translated intron sequences between (a) mutants in box7 in "long" form and "short" form strains (which lack the first three introns including the one for the box3 locus); (b) mutants in a subset of box7 mutants and those in box3, and (c) between intron sequences in box7 and a sequence presumably encoded in oxi3. These structural homologies have been analyzed and shown to be referable to sequence homologies in two proteins, one derived from the second intron (box3) in cob and the other from oxi3. The accumulation in certain cob mutants of proteins and of a transcript containing a sequence specified by oxi3 provides additional strong evidence for the previously suggested regulation of oxi3 by the penultimate, box7-containing intron of cob.
Base Sequence↗