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Biomedical subjects

J Saarinen

Publications and source records attributed to J Saarinen.

At least 19 recordsLinked to original sources
PubMed1995

Proteolysis and fusion of low density lipoprotein particles strengthen their binding to human aortic proteoglycans.

Lipid droplets resembling those seen in the extracellular space of the arterial intima were generated in vitro when granule proteases of rat serosal mast cells degraded the apolipoprotein B-100 (apoB-100) component of granule-bound low density lipoprotein (LDL), and the particles fused on the granule surface (Paanenen, K., and Kovanen, P. T. (1994) J. Biol. Chem. 269, 2023-2031). Moreover, the binding of the fused particles to the heparin proteoglycan component of the granules was found to be strengthened. We have now treated LDL particles with alpha-chymotrypsin and examined the strength with which the proteolytically modified LDL binds to human aortic proteoglycans on an affinity column. We found that chymotryptic degradation of the LDL particles triggered particle fusion. The higher the degree of proteolytic degradation, the higher were the degree of fusion and the strength of binding to the aortic proteoglycans. Separation of the proteolyzed particles by size exclusion chromatography into two fractions, unfused and fused particles, and analysis of their binding strengths revealed that not only the fused but also the unfused proteolyzed particles bound more tightly to the proteoglycans than did the native LDL particles. To investigate the mechanism underlying this increase in binding strength, we attached [13C]dimethyl groups to the lysines and used NMR spectroscopy to quantify the active lysine residues of apoB-100, which are thought to be located in basic areas of apoB-100 and involved in binding of LDL to proteoglycans. Analysis of the 13C-labeled particles showed that, despite loss of apoB-100 fragments from the particles, the number of active lysine residues in the unfused proteolyzed particles had not decreased. In the fused proteolyzed particles, the number of active lysine residues was markedly increased. Thus, proteolytic fusion appears to increase the number of basic domains of apoB-100, which would explain the observed increase in the strength of binding of the modified LDL particles to arterial proteoglycans. Since the fused particles resemble the small lipid droplets found in the atherosclerotic arterial intima, this LDL modification offers a plausible mechanism for the focal accumulation of lipid droplets in the extracellular proteoglycan matrix during atherogenesis.

Aorta↗
PubMed1995

Visual search at different spatial scales.

Treisman and Gelade's (1980) feature-integration model claims that the search for separate ("primitive") stimulus features is parallel, but that the conjunctions of those features require serial scan. Recently, evidence has accumulated that parallel processing is not limited to these "primitive" stimulus features, but that combinations of features can also produce parallel search. In the experiments reported here, the processing of feature conjunctions was studied when the stimulus features of a combination were at different spatial scales. The patterns in the search array were composed of three cross-shaped or T-shaped (local) elements, which formed an oblique bar (the global pattern) 45 deg or 135 deg in orientation. When the target and distractors differed from each other at one spatial scale only (either in the bar orientation or in the shape of the local elements), target detection was independent of the number of distractors, i.e., the search was parallel. In the conjunction task, in which the target and distractors were defined as the combinations of the bar orientation and the element shape, i.e., both spatial scales were relevant, the detection of the target required slow serial scrutiny of the search array. It is possible that the conjunction search could not be performed in parallel because switches between the two scales (or spatial frequency channels) are linked to attention and the task required the use of both scales in order to find the target.

Adult↗
PubMed1995

Ideological and logistical barriers to the development of nursing research: real or imagined?

Australian nurses sit amidst a treasure-trove of developing knowledge, and yet are dragging their feet when it comes to nursing research. Barriers or 'perceived' barriers to the development of nursing research in this country are explored. These include ideological concerns, economic constraints, and infrastructural factors. A set of recommendations, which may assist nurses in attaining a research profile in keeping with the status of a profession is offered.

Attitude of Health Personnel↗
PubMed1995

The incidence of postoperative deep vein thrombosis in vascular procedures. FINNVASC Study Group.

This survey aimed to estimate the rate of deep venous thrombosis (DVT) in an unselected population treated for peripheral vascular diseases. The study comprised 7533 patients on the nationwide Finnish vascular registry (FINNVASC) during two-years study period. Thirty-four (0.45%) patients were reported to have a postoperative thrombosis. Thirty-two (94%) of these had undergone vascular procedures involving the infrarenal aorta or arteries in the lower extremities. There was no difference in the occurrence of determinants (diabetes, hypertension etc.) when the group with postoperative DVT was compared to the rest of the patients on the registry. The procedures involving the lower extremity seem to carry a higher risk of postoperative DVT. In this type of surgery special attention should be focused on DVT prophylaxis.

Adolescent↗
PubMed1992

Representation of abstract attributes of auditory stimuli in the human brain.

Representations of abstract attributes of auditory stimuli in the human brain were demonstrated using the mismatch negativity (MMN), an event-related potential component elicited by a change in a repetitive sound. Stimuli were pairs of sinusoidal tones. There were two types of tone pairs in each block, standard (p = 85%) and deviant pairs (p = 15%), delivered in a random order. Standard and deviant tone pairs differed only in the direction of within-pair frequency change. In addition, the frequency levels of both the standard and deviant pairs varied randomly within a wide range in a block; thus the standard pairs shared the direction of the within-pair frequency change but not the absolute frequency level. Correspondingly, the deviant pairs only shared the opposite direction of the within-pair change. Nevertheless, the deviant tone pairs elicited MMN, implying that even the direction of the within-pair frequency change of the standard stimuli, and not just their absolute frequencies, developed a neural representation.

Acoustic Stimulation↗
PubMed1991

The speed of attentional shifts in the visual field.

The scanning speed of focal visual attention was measured directly by flashing a sequence of two, three, or four numerals one by one at random retinal positions and at a distance from each other to avoid interference between the numerals. Each numeral was followed by a mask pattern so the observers had to move their focal attention in the visual field in synchrony and at the same speed as the presentation rate of the numerals in order to recognize every numeral in the stimulus sequence. Observers could recognize the numerals orders of magnitude above the theoretical chance level of performance even when the presentation rate was as fast as 33 ms per numeral. However, the temporal order of the numerals was perceived rather poorly at the fast presentation rates and for the sequences of four numerals.

Attention↗
PubMed1989

Analysis of spatial structure in eccentric vision.

The analysis of spatial structure, ie, the encoding of relative positions between pattern elements, was studied in central and eccentric vision. In a two-alternative forced-choice task the observer had to discriminate between two patterns consisting of short line segments. At each trial the two patterns were flashed for 140 msec and the observer indicated whether the patterns were identical or mirror symmetric. Psychometric functions were measured by changing pattern size at each eccentricity in order to find the threshold size allowing 75% of correct responses. The scaling factor, required for discriminating between mirror symmetric and identical patterns independent of eccentricity, was found to be similar to the size-scaling proposed by Levi et al (Vision Res 25:963, 1985) for vernier acuity tasks.

Differential Threshold↗
PubMed1988

Detection of mirror symmetry in random dot patterns at different eccentricities.

Differences between central and eccentric vision in the detection of mirror symmetry were investigated using patterns consisting of small dots. In each trial, a dot pattern was flashed for 140 msec and the subject had to decide whether the upper and lower parts of the dot pattern contained mirror symmetric pairs or whether the dots were distributed totally randomly. Detectability of mirror symmetry declined with increasing eccentricity when the retinal size of the dot patterns was constant at different eccentricities and when the size of the patterns in eccentric vision was size-scaled by the cortical magnification factor derived from the frequency of ganglion cells (M-scaling). The drop in detectability was more rapid for constant-size patterns than for M-scaled patterns. The results seem to support the notion that the encoding of positional information in eccentric vision is inferior to that of central vision even when the test patterns are M-scaled.

Form Perception↗
PubMed1988

The effect of exposure duration on the analysis of spatial structure in eccentric vision.

There is some evidence from grating experiments that the transient presentation of a stimulus pattern interferes with the encoding of positional relationships between pattern elements (i.e. the analysis of spatial structure) more in eccentric vision than in central vision. The present study investigated the effect of exposure duration on the analysis of spatial structure in eccentric vision using a task in which the observer discriminated between two mirror symmetric patterns consisting of short line segments. In each trial, the two patterns were flashed for 140 or 500 ms, and the observer had to decide whether the patterns were identical or mirror symmetric. Both constant-size and size-scaled patterns were used in eccentric vision. The longer exposure duration slightly increased the proportion of correct responses in eccentric vision but performance remained distinctly inferior to that in central vision.

Humans↗
PubMed1988

Rapid discrimination of visual patterns in children and adults.

Rapid visual discrimination in children (9 to 11 yr.) and adults was investigated using two tasks in which the subject had to search for a target pattern embedded in 35 background patterns. The time available for inspecting the search arrays was altered by varying the stimulus duration. In one task, there was a large difference in the feature or 'texton' content of patterns between the target and the background; in the other, this difference was small. In the first task, the children could detect the target pattern in a briefly flashed search array with high accuracy, because the target 'popped out' perceptually from the array, but in the second task the same detection rate was not reached until the stimulus duration was much longer, since a serial searching strategy was required. Results achieved by children and adults were similar. It seems that serial visual search is as efficient in children as in adults.

Adult↗
PubMed1988

Rapid discrimination of Julesz's texton patterns in patients with cerebral lesions.

Rapid visual discrimination in patients with unilateral cerebral lesions was investigated using a search task. Both the exposure duration of search arrays and the difference in the texton content between the target pattern and the background patterns were varied. Patients could detect the targets with a large texton difference more rapidly than the targets with a small difference.

Brain Diseases↗
PubMed1987

Perception of positional relationships between line segments in eccentric vision.

The encoding of positional relationships between pattern elements in eccentric vision was studied with different patterns consisting of the same short line segments in different positions. In each trial two stimulus patterns were flashed one above the other and the subject had to decide whether the patterns were identical or mirror symmetric (experiment 1) or whether the patterns were the same or different (experiments 2 and 3). The ability to discriminate between identical and mirror symmetric patterns was reduced in eccentric vision, even when the patterns were size-scaled according to the cortical magnification factor and thus the patterns were similarly visible at the different eccentricities. The results agree with the notion that eccentric vision is inferior to central vision in tasks which require proper encoding of information about the relative positions of pattern elements.

Attention↗
PubMed1987

Texture discrimination at different eccentricities.

Differences in preattentive texture discrimination between central vision and peripheral vision were studied with textures composed of random dots. The subject had to discriminate between two textures whose first-order statistics were kept identical but whose second-order statistics were different. For textures of constant retinal size the discrimination was easy in central vision, but the decrease of visual acuity with increasing eccentricity made the textures unresolvable in peripheral vision. When the textures were scaled by the cortical magnification factor derived from the frequency of retinal ganglion cells so that the calculated neural representations of the textures became similar at different eccentricities, texture discrimination became independent of visual field location. This indicates that preattentive texture discrimination based on differences in second-order statistics of random dots operates similarly in central vision and peripheral vision.

Discrimination, Psychological↗
PubMed1985

Self-organized formation of colour maps in a model cortex.

A report is presented of computer simulations which demonstrate the applicability of self-organization principles to the formation of a cortical colour map. A two-dimensional array of cortical units can be shown to become selectively sensitive to different colour stimuli in an orderly fashion. The precortical part of the simulation model contains three wavelength-sensitive receptors with overlapping sensitivity distributions, and a simple opponent processing stage. Each cortical unit receives the same activity from the precortical stage by adaptive connections. Initially the connections are arbitrary; during self-organization they are changed so that different way. Self-organization of the connections can be shown to take place even when the stimulation of the receptors is totally random, ie the wavelength and purity (and in some simulations the distribution) of each stimulus are selected randomly.

Color Perception↗