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Biomedical subjects

M J Nissen

Publications and source records attributed to M J Nissen.

13 recordsLinked to original sources
PubMed1991

Procedural learning is impaired in Huntington's disease: evidence from the serial reaction time task.

The purpose of the study was to test the hypothesis that Huntington's disease (HD) is associated with impairment of procedural learning. We identified 13 patients with mild to moderate HD whose manual performance was still sufficiently intact to assess learning on the serial reaction time (SRT) task. Twelve age-matched neurologically normal control subjects were studied as well. The SRT task was a four-choice reaction time task in which the stimuli followed a sequence (10 items in length) which repeated itself 10 times during each of the first four blocks of trials. During the fifth block of trials, the stimuli were random. Learning was manifested by a reduction in response latency over the first four blocks and an increase in response latency in the fifth (random) block. Learning in this task has been demonstrated in other amnesics of other etiologies. The HD patients were significantly impaired on sequence-specific learning, using the log-transformed reaction time data (P less than 0.004). In addition, in an individual-by-individual analysis, five of the HD patients and none of the control subjects failed to show sequence-specific learning, a difference in proportions that was significant (P less than 0.04). No feature of the standard cognitive or motor assessment of the HD patients was associated with efficacy of procedural learning. HD, including patients with mild disease, was associated with a deficit in procedural learning, consistent with the hypothesis that the striatum plays a critical role in supporting procedural learning.

Adult↗
PubMed1990

Attentional processing and the independence of color and orientation.

Judgments of the color and shape of a stimulus specified by a cue indicating its location demonstrate stochastic independence. Evidence for the independence of color and orientation was obtained when the cue followed stimulus offset immediately, the cue followed stimulus offset by 2 s, and when either a central or peripheral precue focused attention on the cued stimulus at the time of its presentation. It appears that an object's color and orientation are represented independently even following the attentional focusing thought to support feature integration.

Adolescent↗
PubMed1989

Selective attention in Alzheimer's disease: characterizing cognitive subgroups of patients.

Picture recognition was studied in 20 patients with AD and in 20 control subjects, using a procedure that matched these groups for initial performance. The groups did not differ significantly in overall forgetting, although 10 patients displayed improved recognition performance 72 hr after learning. These same patients were impaired in a test of attentional focusing, as revealed by post hoc analyses. A predictive experiment involving 20 new patients with AD confirmed the initial findings: a subgroup of patients displayed improved recognition performance 72 hr after learning and impairments in attentional focusing. Neuropsychological tests thus identify a subgroup of patients with impaired selective attention, perhaps related to locus coeruleus neuropathology.

Aged↗
PubMed1989

Explicit and implicit remembering: when is learning preserved in amnesia?

Amnesic patients can learn and retain a variety of skills. To investigate what distinguishes tasks that are within the learning abilities of amnesic patients from those that are not, we administered two tests to individuals with Korsakoff's syndrome and two control groups. One was a visual reaction time task with an embedded repeating sequence of stimulus positions. Response times of Korsakoff patients indicated that they learned this sequence and retained it normally for a week. The second task was a tactual stylus maze in which all blind alleys were blocked. Korsakoff patients were impaired in learning this maze, as assessed by the time required to trace it. Differences between the two tasks are outlined and the implications of these differences are discussed.

Adult↗
PubMed1989

On the development of procedural knowledge.

Amnesic patients demonstrate by their performance on a serial reaction time task that they learned a repeating spatial sequence despite their lack of awareness of the repetition (Nissen & Bullemer, 1987). In the experiments reported here, we investigated this form of procedural learning in normal subjects. A subgroup of subjects showed substantial procedural learning of the sequence in the absence of explicit declarative knowledge of it. Their ability to generate the sequence was effectively at chance and showed no savings in learning. Additional amounts of training increased both procedural and declarative knowledge of the sequence. Development of knowledge in one system seems not to depend on knowledge in the other. Procedural learning in this situation is neither solely perceptual nor solely motor. The learning shows minimal transfer to a situation employing the same motor sequence.

Adult↗
PubMed1989

Implicit learning of new verbal associations.

Implicit learning of a series of new verbal associations was studied in four experiments. The first two experiments demonstrated that learning of a repeating sequence of verbal stimuli may occur without awareness, but only when the stimulus-response mapping requires an attention-demanding activity: Subjects who were unaware of the sequence learned when instructed to categorize the stimuli, but not when instructed simply to read them. However, in both situations, unaware subjects performed no better than untrained control subjects in expressing their knowledge of the sequence explicitly. In Experiments 3 and 4, subjects showed implicit learning when the task involved either motor responses to verbal stimuli or verbal responses to spatially arranged stimuli. These findings are discussed in terms of the conditions under which implicit learning can be obtained. First, they demonstrate implicit learning of a set of new associations in the verbal domain. Second, the data suggest that attention is important in implicit learning. Finally, the degree of interitem organization that is familiar preexperimentally seems to partially determine the amount of implicit learning.

Adult↗
PubMed1988

Selective attention in Alzheimer's disease: CSF correlates of behavioral impairments.

CSF levels of HVA, 5-HIAA, and free MHPG, the major metabolites of dopamine, serotonin, and norepinephrine respectively, were measured in 22 patients with AD. These 22 patients were also administered tests of picture-recognition and attentional focusing as part of an earlier experiment. A significant association between deficits in attentional focusing and reduced levels of free MHPG in CSF was noted. These results suggest that behavioral measures can identify patients with noradrenergic involvement.

Aged↗
PubMed1988

Memory and awareness in a patient with multiple personality disorder.

We studied an individual with multiple personality disorder in whom each of several personalities claimed to have no direct awareness of the others and to be unable to consciously remember the experiences of other personalities. A broad selection of implicit and explicit memory tests was used to determine the extent to which one personality had access to knowledge acquired by another and the circumstances in which that knowledge would be expressed. The implicit assessment of memory was a necessary but not sufficient condition for demonstrating interpersonality access. The degree of compartmentalization of knowledge in this patient depended largely on whether the interpretation of presented information was likely to differ across personalities.

Awareness↗
PubMed1987

Implicit learning in patients with probable Alzheimer's disease.

The purpose of the present study was to determine whether patients with probable Alzheimer's disease (AD) were capable of implicit procedural learning. AD patients and elderly control subjects were given a serial visual reaction time task with an embedded repeating sequence. The AD patients responded more slowly than the controls, but many nonetheless showed learning of the repeating sequence. Patients who failed to learn the sequence were similar in age and overall severity of dementia to those who learned, but they scored lower on some tasks of nonverbal reasoning.

Aged↗
PubMed1987

Neurochemical dissociation of memory systems.

The administration of scopolamine, an anticholinergic drug, reduced the ability to recall and recognize stimuli presented previously--abilities thought to require declarative memory. In contrast, measures of procedural memory were unaffected by scopolamine: performance on a serial reaction time task incorporating a repeating stimulus and response sequence showed no difference in acquisition and retention of the sequence after scopolamine or saline. These results suggest that the cholinergic system is required for declarative but not procedural memory.

Adult↗
PubMed1979

Chromatic information processing.

The investigation of visual processing mediated solely by chromatic information requires conditions preventing a subject's use of the luminance differences normally accompanying a chromatic change. In Experiment 1, which involved a discriminative reaction time (RT) task, chromatic and white stimuli of the same luminance were presented on a dimmer achromatic background. Subjects were instructed to respond only to the chromatic stimuli. RT was slowest at 570 nm and somewhat faster to short wavelengths than to long wavelengths. In Experiment 2, which compared two discriminative RT tasks, RT was faster when subjects responded to color than when they responded to white. Experiments 3 and 4 demonstrated that a brighter white surround decreased the perceived brightness of chromatic stimuli as well as their perceptual similarity to white, but did not affect RT. The results are discussed in terms of the response strength of the chromatic processing channel.

Color Perception↗
PubMed1979

Luminace, not brightness, determines temporal brightness enhancement with chromatic stimuli.

Brightness-duration relations for chromatic stimuli were studied using three pulse-to-background luminace relations: chromatic equal-luminance pulses (3.2 cd/m2) were presented as increments of 0.3 or 1.0 log units above a lower luminance achromatic background, or were presented in hue substitution, equated in luminance to the achromatic background, so that no spatio-temporal luminance transients occurred during stimulus presentation. Incremental pulses produced temporal brightness enhancement (the Broca-Sulzer phenomenon), but hue substitution pulses did not. Temporal brightness enhancement thus depends upon the occurrence of luminance transients and cannot be produced by pulsed-to-background brightness differences associated solely with chromaticity differences.

Color Perception↗