Search PubMed⌕ Search

Biomedical subjects

D Smilek

Publications and source records attributed to D Smilek.

11 recordsLinked to original sources
PubMed2001

Synaesthetic photisms influence visual perception.

When C, a digit-color synaesthete, views black digits, she reports that each digit elicits a highly specific color (a photism), which is experienced as though the color was externally projected onto the digit. We evaluated this claim by assessing whether C's photisms influenced her ability to perceive visually presented digits. C identified and localized target digits presented against backgrounds that were either congruent or incongruent with the color of her photism for the digits. The results showed that C was poorer at identifying and localizing digits on congruent than incongruent trials. Such differences in performance between congruent and incongruent trials were not found with nonsynaesthete control participants. These results suggest that C's colored photisms influence her perception of black digits. We propose a model in which color information influences the perception of digits through reentrant pathways in the visual system.

Adult↗
PubMed2001

Perception without awareness: perspectives from cognitive psychology.

Four basic approaches that have been used to demonstrate perception without awareness are described. Each approach reflects one of two types of experimental logic and one of two possible methods for controlling awareness. The experimental logic has been either to demonstrate a dissociation between a measure of perception with awareness and a measure that is sensitive to perception without awareness or to demonstrate a qualitative difference between the consequences of perception with and without awareness. Awareness has been controlled either by manipulating the stimulus conditions or by instructing observers on how to distribute their attention. The experimental findings based on all four approaches lead to the same conclusion; namely, stimuli are perceived even when observers are unaware of the stimuli. This conclusion is supported by results of studies in which awareness has been assessed with either objective measures of forced-choice discriminations or measures based on verbalizations of subjective conscious experiences. Given this solid empirical support for the concept of perception without awareness, a direction for future research studies is to assess the functions of information perceived without awareness in determining what is perceived with awareness. The available evidence suggests that information perceived without awareness both biases what stimuli are perceived with awareness and influences how stimuli perceived with awareness are consciously experienced.

Attention↗
PubMed2001

Differential attentional guidance by unattended faces expressing positive and negative emotion.

Four experiments were conducted to evaluate whether focal attention can be guided by an analysis of the emotional expression in a face. Participants searched displays of 7, 11, 15, and 19 schematic faces for the location of a unique face expressing either a positive or a negative emotion located among distractor faces expressing a neutral emotion. The slopes of the search functions for locating the negative face were shallower than the slopes of the search functions for locating the positive face (Experiments 1A and 2A). When the faces were inverted to reduce holistic face perception, the slopes of the search functions for locating positive and negative faces were not different (Experiments 1B and 2B). The results suggest that the emotional expression in a face can be perceived outside the focus of attention and can guide focal attention to the location of the face.

Adult↗
PubMed2000

Does unattended information facilitate change detection?

Changes between alternating visual displays are difficult to detect when the successive presentations of the displays are separated by a brief temporal interval. To assess whether unattended changes attract attention, observers searched for the location of a change involving either a large or a small number of features, in pairs of displays consisting of 4, 7, 10, 13, or 16 letters (Experiment 1) or digits (Experiments 2 and 3). Each display in a pair of displays was presented for 200 ms, and either a blank screen (Experiments 1 and 2) or a screen of equal luminance to the letters and digits (Experiment 3) was presented for 80 ms between the alternating displays. In all experiments, the search function for locating the larger change was shallower than the search function for locating the smaller change. These results indicate that unattended changes play a functional role in guiding focal attention.

Adult↗
PubMed1992

Evidence that tolerance to cultured thyroid allografts is an active immunological process. Protection of third-party grafts bearing new antigens when associated with tolerogenic antigens.

We studied the tolerance phenomenon that develops in long-term recipients of cultured thyroid allografts. Allogeneic mouse thyroids were cultured under hyperbaric oxygen or acidic conditions and then transplanted beneath the kidney capsule of C57BL/6 recipients. Donors differed from the recipients in minor antigens alone, major histocompatibility complex antigens alone, or both. At 35-77 weeks after the first cultured graft, recipients received two more cultured grafts under the capsule of the opposite kidney and were immunized with donor spleen cells (SC). At 5 weeks after the second transplantation, we observed that whereas second grafts carrying new antigens alone were rejected, second grafts carrying new antigens in association with antigens in the first graft were significantly protected. In another set of experiments, normal mice became tolerant to cultured allografts after 2 weeks in parabiosis with tolerant individuals. Tolerant mice showed reduced specific in vivo and in vitro cytotoxic T lymphocyte responses. However, the frequency of CTL precursors of tolerant mice was the same as in normal mice. The reduced in vitro CTL responses were restored to normal levels by the addition of a lymphokine rich medium. Also, we observed that the injection of specifically activated immune SC caused the rejection of cultured allografts in normal but not in tolerant recipients. We conclude that the tolerance that develops in recipients of cultured allografts is an active immunological process that affects the activation and effector function of CTL.

Animals↗
PubMed1991

An immune response defect due to low levels of class II cell surface expression. Analysis of antigen presentation and positive selection.

The effects of quantitative differences in class II cell surface expression have been difficult to address in intact animals. This study uses several lines of H-2s/s mice carrying an A beta k transgene that differ significantly in terms of class II cell surface expression. Due to inefficient chain pairing, mice carrying 60 to 65 copies of this transgene express only low levels of A alpha s/A beta k on the cell surface, and cell surface expression of the endogenous A alpha s/A beta s complex (and total Ia) is severely reduced (to 7-15% control levels). The significant decrease in class II cell surface expression in the thymic cortex of these mice did not affect the frequency of peripheral T cells expressing at least 10 distinct TCR V beta chains. However, T cell proliferative responses to the A alpha s/A beta s-restricted peptide MBP 89-101 were abrogated in high copy number A beta k mice. Experiments using bone marrow chimeras demonstrated that both inefficient Ag presentation and failure to positively select appropriate T cells contributed to this lack of response. Inefficient Ag presentation was clearly the dominant defect, and the density of class II cell surface expression required for positive selection appeared to be quite low.

Animals↗
PubMed1991

Competitive inhibition of antigen presentation in animal models of autoimmune disease.

Competition between peptides for binding to class II major histocompatibility complex (MHC) molecules has been demonstrated both in vitro and in vivo. Peptide competition may provide a way to interfere with T cell activation in the treatment of autoimmune diseases. It may be possible to provide a substitute 'blocking' peptide to compete for presentation of an autoantigenic peptide to T cells. The approach described is a general one, which may be applicable to a number of T cell mediated MHC-linked autoimmune diseases, and to other undesirable immune responses. So far, peptide competitors have only been successfully used in the prevention of experimental autoimmune encephalomyelitis (EAE). Whether or not this approach will work in treating spontaneous disease models remains to be tested, although work in other test systems is encouraging.

Animals↗
PubMed1981

Induced tolerance in F1 rats to anti-major histocompatibility complex receptors on parental T cells. Implications for self tolerance.

The immunogenicity of cell surface markers associated with specific anti-major histocompatibility complex (MHC) alloreactivity of rat peripheral T lymphocyte subpopulations has been demonstrated in the past by the ability of such cell populations to induce a profound and specific resistance to systemic graft-vs.-host (GVH) disease in adult rats. Our studies demonstrate that these specificity-associated anti-MHC parental strain T cell markers are also tolerogenic; if small numbers of parental strain T cells are administered to newborn F1 rats, they result in the specific inability to induce GVH resistance later on in adult life. Moreover, unlike normal animals, these F1 rats are extremely sensitive to systemic GVH disease caused by T cells from the original donor parental strain.

Animals↗