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Biomedical subjects

P M Merikle

Publications and source records attributed to P M Merikle.

At least 19 recordsLinked to original sources
PubMed2002

Synaesthesia: a case study of discordant monozygotic twins.

We describe a study of 11-year-old twin sisters who are physically identical in appearance but who have considerably different conscious experiences. One twin appears to be a synaesthete in that she states that she has specific colour experiences (i.e. photisms) whenever she views, hears or thinks of digits. The other twin does not report such conscious experiences when viewing, hearing or thinking about digits. A genotypic analysis using eight microsatellite loci plus the gender of the twins and their parents confirmed that the twins are monozygotic. A phenotypic analysis using a modification of the Stroop task confirmed that only one twin is a synaesthete. We suggest that the discordance in synaesthesia may be due to either an epigenetic event, X chromosome inactivation, or a mutation of a synaesthesia gene.

Child↗
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↗
PubMed2000

Conscious and unconscious influences of memory: temporal dynamics.

Changes in the conscious and unconscious influences of memory over time were assessed in two experiments by using a variant of the process-dissociation procedure. In both experiments, performance on a stem-completion task was measured under both inclusion and exclusion instructions. Across the two experiments, there were four different retention intervals: 2 minutes, 2 days, 2 weeks, and 2 months. The results indicated that conscious influences decreased systematically across retention interval. In contrast, unconscious influences of memory in the absence of conscious influences increased between 2 minutes and 2 days, and then remained relatively stable from 2 days to 2 weeks to 2 months. These results stand in apparent contrast to those of McBride and Dosher (1999), which showed equal rates of forgetting for conscious and unconscious influences of memory on performance. The implications for models of the relation between conscious and unconscious influences of memory on performance are discussed.

Consciousness↗
PubMed1999

Conscious and unconscious processes: the effects of motivation.

The process-dissociation procedure has been used in a variety of experimental contexts to assess the contributions of conscious and unconscious processes to task performance. To evaluate whether motivation affects estimates of conscious and unconscious processes, participants were given incentives to follow inclusion and exclusion instructions in a perception task and a memory task. Relative to a control condition in which no performance incentives were given, the results for the perception task indicated that incentives increased the participants' ability to exclude previously presented information, which in turn both increased the estimate of conscious processes and decreased the estimate of unconscious processes. However, the results also indicated that incentives did not influence estimates of conscious or unconscious processes in the memory task. The findings suggest that the process-dissociation procedure is relatively immune to influences of motivation when used with a memory task, but that caution should be exercised when the process-dissociation is used with a perception task.

Analysis of Variance↗
PubMed1998

On demonstrating unconscious perception: comment on Draine and Greenwald (1998)

S. C. Draine and A. G. Greenwald (1998) have described a methodology based on regression analysis for demonstrating unconscious perception. They have suggested that their methodology represents a major improvement over existing methodologies. An analysis of their methodology reveals that it is closely related to the classic dissociation paradigm. As such, interpretation of their results is compromised by the same issues concerning the measurement of awareness that have plagued all previous attempts to use the dissociation paradigm to demonstrate unconscious perception in the complete absence of conscious perception.

Cognition↗
PubMed1998

Selective attention: a reevaluation of the implications of negative priming.

The notion that inhibitory processes play a critical role in selective attention has gained wide support. Much of this support derives from studies of negative priming. The authors note that the attribution of negative priming to an inhibitory mechanism of attention draws its support from a common assumption underlying priming procedures, together with the procedure that has been used to measure negative priming. The results from a series of experiments demonstrate that selection between 2 competing prime items is not required to observe negative priming. This result is demonstrated across several experiments in which participants named 1 of 2 items in a second display following presentation of a single-item prime. The implications of these results for existing theories of negative priming are discussed, and a theoretical framework for interpreting negative priming and several related phenomena is forwarded.

Adult↗
PubMed1996

Memory for unconsciously perceived events: evidence from anesthetized patients.

Studies investigating memory for events during anesthesia show a confusing pattern of positive and negative results. To establish whether there are any consistent patterns of findings across studies, we conducted a meta-analysis of the data from 2517 patients in 44 studies. The meta-analysis included two measures of the effects of positive suggestions on postoperative recovery: (a) the duration of postoperative hospitalization and (b) the amount of morphine administered via patient-controlled anesthesia, as well as two measures of memory for specific information presented during anesthesia: (c) direct tests and (d) indirect tests. The meta-analysis indicated that positive suggestions presented during anesthesia have little or no effect on postoperative recovery. On the other hand, the meta-analysis showed that specific information is remembered following surgery, as long as testing is not delayed longer than 36 h. Studies of memory for events during anesthesia provide a useful avenue for exploring unconscious cognition.

Anesthesia, General↗
PubMed1996

Information processing during general anesthesia: evidence for unconscious memory.

Memory for words presented during general anesthesia was studied in two experiments. In Experiment 1, surgical patients (n = 80) undergoing elective procedures under general anesthesia were presented shortly before and during surgery with words via headphones. At the earliest convenient time after surgery (within 5 h) and 24 h later, memory was tested by asking patients to complete auditorily presented word stems with the first word that came to mind and to leave out words they remembered having heard earlier (exclusion task). Moreover, patients were requested to perform a "yes/no" forced-choice recognition task to assess recognition memory for both the pre- and intraoperative words. Memory for the material presented during anesthesia was demonstrated immediately after surgery and 24 h later by means of both tasks. In a second similar experiment (n = 80), the results were replicated. These findings show that anesthetized patients can process information that was presented intraoperatively.

Adolescent↗
PubMed1995

Measuring the relative magnitude of unconscious influences.

As an alternative to establishing awareness thresholds, stimulus contexts in which there were either greater conscious or greater unconscious influences were defined on the basis of performance on an exclusion task. Target words were presented for brief durations and each target word was followed immediately by its three-letter stem. Subjects were instructed to complete each stem with any word other than the target word. With this task, failures to exclude target words indicate greater unconscious influences, whereas successful exclusion indicates greater conscious influences. Conscious influences were dominant at long durations (e.g., 214 ms), but unconscious influences were dominant at short durations (e.g., 50 ms). Performance on the exclusion task successfully predicted both qualitative differences in Stroop priming and qualitative differences in recognition memory previously associated with the different effects of conscious and unconscious influences. Taken together, these results demonstrate that an exclusion task allows both unconscious and conscious influences to be defined in terms of significant deviations from baseline performance. As such, exclusion tasks provide a method for distinguishing conscious from unconscious influences that does not require establishing thresholds for null awareness.

Adult↗
PubMed1992

Subliminal self-help audiotapes: a search for placebo effects.

Subliminal self-help audiotapes to aid weight loss were evaluated to determine if their apparent effectiveness is due to a placebo effect. All subjects were female students or staff who were both overweight and believed in the possible effectiveness of subliminal audiotapes. Three different groups of subjects were tested: One group listened to subliminal audiotapes purchased directly from a manufacturer, the 2nd group listened to comparable placebo tapes, and the 3rd group did not listen to any tapes at all. Each subject in each group was weighed once each week for 5 weeks. All 3 groups of subjects lost weight, and the average amount of weight lost by each group was approximately equivalent. These results provide no evidence that regular use of subliminal audiotapes leads to a placebo effect. Rather, the results suggest that regular use of subliminal audiotapes may simply make subjects more conscious of their weight.

Adolescent↗
PubMed1992

False recognition and perception without awareness.

Jacoby and Whitehouse (1989) demonstrated that the probability of calling new test words "old" (i.e., false recognition) is biased by context words. When context words were briefly exposed and subjects were not informed of their presence, new words were called "old" more often if the context and test words were identical than if the context and test words were different. When the context words were presented at longer exposure durations and subjects were informed of their presence, the opposite pattern of results occurred. In Experiment 1, we replicated the critical qualitative difference across conditions reported by Jacoby and Whitehouse. In addition, the combined results of Experiments 2 and 3 demonstrated that the exposure duration of the context words, and not the instructions to the subjects, is the primary factor determining which pattern of false recognition occurs. However, in contrast with the findings of Jacoby and Whitehouse, both patterns of false recognition were associated with significant recognition memory for the context words. The latter finding presents problems for any interpretation of false recognition, which implies that the briefly exposed context words are perceived without awareness.

Adult↗
PubMed1990

Recognition and lexical decision without detection: unconscious perception?

Stimulus detection and concurrent measures of stimulus recognition were compared to establish whether perception occurs in the absence of detection. The target stimuli were familiar words (Experiments 1 and 2), nonwords (Experiment 3), or both words and nonwords (Experiment 4). On each trial, either a stimulus or a blank field was presented. Ss first decided whether a stimulus had been presented and then made either a forced-choice recognition decision (Experiments 1, 2, and 3) or a lexical decision (Experiment 4). Both words and nonwords were recognized and discriminated following correct detections (i.e., hits). However, in the absence of stimulus detection (i.e., misses), only words were recognized or discriminated. These qualitatively different patterns of results following hits and misses for words and nonwords suggest that stimulus detection may provide an adequate measure of conscious awareness.

Adult↗
PubMed1988

Global precedence in attended and nonattended objects.

In four experiments we evaluated whether there is a priority in early perceptual analysis for the global aspect of a nonattended, visual, compound stimulus. In all experiments, two objects were distinguished by being enclosed in either a square or a circle, and each object consisted of a larger letter constructed from smaller letters. Attention was directed to one of the two objects on the basis of either the square/circle distinction (Experiments 1, 2, and 3) or a visual precue (Experiment 4). In agreement with previous findings, for attended objects, the global aspect was identified faster and was more difficult to ignore than the local aspect. However, for nonattended objects, no evidence was found for an overall priority in perceptual processing leading to identification of the global aspect. Rather, the results indicate that there is a priority in perceptual processing for the general category of the global information contained within nonattended objects. Although the results provide some support for the view that global information receives priority during early perceptual analysis, aspects of the results are more consistent with postidentification accounts of global precedence.

Adult↗