Biomedical subjects

S Krekling

Publications and source records attributed to S Krekling.

14 recordsLinked to original sources

PubMed1996

Does melatonin have an effect on cognitive performance?

Exogeneous melatonin causes phase shifts of circadian rhythms, reduces core body temperature, and induces drowsiness, but dispute still surrounds the hormone's effect on cognitive performance. Using a N = 1 double-blind alternating treatments design, daytime performance on four cognitive tests (logical reasoning, serial add/subtract, visual-spatial, and four-choice reaction time tasks) was measured after PO doses of placebo and 1.6 mg melatonin. Serum melatonin and core body temperature were also recorded. Performance was measured during time windows corresponding to the serum melatonin peak and the temperature trough respectively, following melatonin administration. The data showed that performance speed and accuracy measures were not affected during the serum melatonin peak, but that reaction times on all cognitive tasks increased substantially during the temperature trough. These results suggest that circulating melatonin has no direct and immediate effect on cortical information processing, and that the reduction in cognitive processing speed during body temperature trough occurs as a consequence of the hormone's hypothermic properties, causing a slowing down of cerebral processing speed.

Adult↗

PubMed1994

Directional biases in adults' performance on a multiple-choice water-level task.

Performance data on the water-level task were collected on a multiple-choice test requiring 417 adult subjects to choose the one item that represented the waterline of still water in a tilted vessel. Except for the item showing the waterline horizontal, waterlines were drawn oriented +/- 8 degrees, +/- 16 degrees, +/- 24 degrees, and +/- 32 degrees referenced to the horizontal. Analyses of errors from 284 subjects who did not achieve a perfect test score showed that 73% of all errors were made on negatively signed items. Further, among subjects who erred on all trials (n = 128), the majority were remarkably systematic in making their errors, consistently (six out of six trials) choosing items with a negative sign (56%) or items with a positive sign (13%). The predominant negative directional bias suggests that most adult subjects who completely lack an adequate understanding of the invariant horizontality of water were basing their choices on the belief that water tends to climb obliquely towards the brim of the tilted vessel.

Adult↗

PubMed1992

Observational training improves adult womens' performance on Piaget's water-level task.

Among women university students who lacked conceptual understanding of the principle that the surface of still water is always horizontal, a specific task procedure designed to optimize self-discovery of the principle proved effective. Successful learning was reflected in more accurate responses on an adjustment task and by a significant increase (p less than .01) in the number of subjects able to verbalize a correct strategy. In contrast to previous research the results show that adult womens' performance on the water-level task can be improved by observational training, suggesting that the female lag in spatial skills may depend on experiential factors.

Attention↗

PubMed1989

Tactual learning and cross-modal transfer of an oddity problem in young children.

The ability to solve tactual oddity problems, and transfer of oddity learning across the visual and the tactual modalities, was studied in 3- to 8-year-old children (N = 294). Oddity tasks consisting of one odd and two equal objects were made from stimuli that were easily discriminated visually and tactually. The results showed that tactual oddity learning increased gradually with age. The growth in tactual performance begins later than visual, suggesting that children are more adept at encoding visual stimulus invariances or relational properties than tactual ones. Bidirectional cross-modal transfer of oddity learning was found, supporting the suggestion that such transfer occurs when training and transfer oddity tasks share a common vehicle dimension. The cross-modal effect also shows that oddity learning is independent of a specific modality-labeled perceptual context. Our results are consistent with the view that development of oddity learning depends on a single rather than a dual process, and that the oddity relation may be treated as an amodal stimulus feature.

Attention↗

PubMed1984

Spatial summation in subregions of simple-cell receptive fields in cat striate cortex as a function of slit length.

Spatial summation along the optimum stimulus orientation in subregions of simple-cell receptive fields in cat striate cortex was studied quantitatively by measuring the response to stationary light slits of variable length. Before summation analysis, the cell's discharge field was mapped by flashing a test slit on and off in a sequence of positions through the receptive field. A static activation procedure was used to determine the extension of subregions of the receptive field where light stimulation increased (enhancement) or decreased (suppression) the firing rate. An activation slit in the optimum orientation was positioned in the most responsive position of the discharge field and the effects of a parallel test slit, in a series of broadside positions, were assessed from the changes induced in the discharge elicited by the activation slit. Length-response curves for on and off responses were made by positioning a test slit in the respective subregions of the discharge field. The activation procedure was used to make length-response curves for suppression. A test slit of variable length was positioned in a suppression region defined by the activation profiles and an activation slit of fixed length was centred in the most responsive discharge field position. Length summation was found for all cells, both with respect to on and off responses, and suppression. The curves for on and off responses had a maximum value beyond which the response declined or levelled off, but some cells had a secondary, more shallow increase beyond an initial, steeply rising part. Similar properties were found for summation of suppression except that the effects were opposite in sign. Curves made for both on and off regions in the same cell often differed in shape. Such differences were also found when length-response curves made in different suppression regions of the same cell were compared. The various length-summation functions were explained by a model presuming that simple-cell receptive fields consist of partially overlapping non-concentric excitatory and inhibitory fields. This arrangement would also explain why length-response curves in various subregions often had different shapes.

Animals↗

PubMed1983

Spatial summation in the receptive field of simple cells in the cat striate cortex.

Spatial summation was studied quantitatively through width response curves made with an optimally oriented test slit of variable width, and by comparing the response to combined presentation of several parallel slits with the response to each slit alone. Prior to summation analysis, the cell's discharge field (DF) was mapped by presenting a test slit ON and OFF across the receptive field. Activation profiles, showing the extension of subregions where light stimulation increased (enhancement) or decreased the firing rate (suppression), were made by presenting an optimally oriented activation slit in the most responsive DF-position. Against this activity the effects of a parallel test slit were determined in a series of broadside positions. Width response curves were made over the subregions of the DF and the activation profiles. Spatial summation was found in all cells, but the width of the summation region was smaller than the width of the subregions in the respective profiles. The width of the summation region was related to the degree of activation rather than to specific locations within the receptive field. The effect produced by several slits presented together deviated from the algebraic sum of the effects produced by each slit alone. Linear summation was rarely found. Accumulated response curves obtained by integration of DF or activation profiles were compared with width response curves to test linearity of summation. Linear summation throughout the whole receptive field was never found. A satisfactory fit was found only over a narrow region showing that summation was linear within a small part of the summation region. Linearity ended near response maxima or minima in the response profiles. The results indicate that the receptive field of simple cells consists of overlapping excitatory and inhibitory fields, and that the exact location and width of enhancement and suppression zones are determined by an activity-dependent balance between excitatory and inhibitory inputs.

Animals↗

PubMed1983