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M Snodgrass

Publications and source records attributed to M Snodgrass.

11 recordsLinked to original sources
PubMed2004

Event-related brain correlates of associative learning without awareness.

Controversy exists about whether associative learning occurs without awareness. In an earlier study using subthreshold (subliminal) stimuli, we reported evidence that such learning could occur as measured by event-related brain potentials [ERP; Cons. Cognit. 6 (1997) 519]. In the present study, we extend these findings by changing several aspects of the methodology in order to provide a more stringent test of this effect and to examine its generality. We used two matched words (murder and cancer) as conditional stimuli (CS); a 100 dB white noise blast as unconditional stimulus (US); a CS-US interval of 3 s; and a full-factorial design with CSs counterbalanced. The conditioning-acquisition phase occurred when the CSs were perceptually unconscious, as confirmed by a subsequent behavioral task. The conditioning-acquisition and postconditioning-extinction phases were examined for ERP evidence of associative learning. The clearest and strongest evidence for associative learning without awareness was observed in the ERP component measures (up to 1 s, poststimulus) in the postconditioning-extinction phase. The CS+ was significantly more positive than the CS- in the P3b-LP component region, which is highly consistent with the results of our earlier study. Differences also were observed in the P1-P2 components. In an unexpected finding, we observed a significant positive slow potential shift for the CS+ in the region between 1 and 3 s poststimulus. We discuss these results and their implications for our understanding of associative learning and awareness.

Adult↗
PubMed2001

Subliminal visual oddball stimuli evoke a P300 component.

OBJECTIVE: To provide evidence that a P300 component can be elicited by subliminal stimuli in an oddball paradigm. METHODS: The words LEFT and RIGHT were presented in a frequent-rare ratio (80-20%), counterbalanced between subjects. Stimuli were presented at the objective detection threshold (d'=0, via unmasked 1 ms presentations), a stringent measure for detecting any conscious perception. RESULTS: A significantly larger amplitude component was found for rare vs. frequent stimulus presentations across electrodes Fz, Cz, and Pz using both a broad 200-900 ms window (F(1,27)=5.75, P<0.012, eta(2)=0.18; one-tailed), and a more narrow 400-760 ms window defined using principal component analysis (F(1,27)=10.10, P<0.002, eta(2)=0.27; one-tailed). No significant component latency effects were found. An analysis of the conscious perception index (d') and the oddball effect (rare-frequent amplitude difference) revealed a negative relationship, further supporting the contention that conscious perception does not account for the finding, and suggesting that any conscious stimulus detection may inhibit this subliminal effect. CONCLUSIONS: Results provide evidence that an endogenous component can be elicited by undetectable subliminal stimuli in an oddball paradigm. Implications are discussed for comparing conscious and unconscious information processing, unconscious learning, and the measurement of ERPs to subliminal stimuli.

Adult↗
PubMed2000

The primary process and the unconscious: experimental evidence supporting two psychoanalytic presuppositions.

The authors report on two experiments designed to test an important feature of the primary process: unconscious categorisation by attributes rather than by relations. These experiments were designed to provide support, independently of the clinical situation, for the presupposition of a psychological unconscious and for the presupposition that unconscious mentation is organised along primary-process lines. Their results were encouraging. They found that (1) unconscious similarity judgements could be made; and (2) these judgements were based on attributes (a primary-process mechanism) rather than relationships (a secondary-process mechanism). This independent evidence, obtained in controlled experimental studies supporting two fundamental psychoanalytic presuppositions, should be welcome news to psychoanalysts, given the continuing criticism from many quarters that basic psychoanalytic ideas lack independent validation. This paper begins with an overview of the primary processes with a special focus on the role of categorisation by attribute, the particular aspect of primary process explored in this study. Next a brief history of previous empirical investigations of primary process is given, following which the current experiments are presented.

Adult↗
PubMed1989

Music absorption and hypnotizability.

The present study investigated differences between high (N = 15), medium (N = 20), and low (N = 16) hypnotizable Ss' involvement in imaginative versus nonimaginative music. Ss were first screened for hypnotizability with the Harvard Group Scale of Hypnotic Susceptibility, Form A (Shor & E. Orne, 1962). In a second session presented as a study of music appreciation, Ss listened to classical music of high and low rated music imaginativeness. Ss' involvement was indexed by absorption, imagery elaboration reported in open-ended essays, and reaction time to a pure tone. High hypnotizable Ss reported more absorption than low hypnotizable Ss, regardless of the imaginativeness level of the music. Ss reported more imagery elaboration in the imaginative than in the low imaginative passages. High hypnotizable Ss tended to differ in their imagery elaboration in response to the imaginative passages but not in response to the nonimaginative passages. Reaction time results were nonsignificant. No sex differences were found. Medium hypnotizable Ss were indistinguishable from both high and low hypnotizable Ss. The findings are generally compatible with J. R. Hilgard's (1970, 1974) construct of imaginative involvement.

Attitude↗
PubMed1987

Goal-directed fantasy, hypnotic susceptibility, and expectancies.

We conducted an initial screening session in which hypnosis was presented as a "test of imagination" and administered with other imagination measures. In a second session, we instructed high- and low-hypnotizable subjects to imagine along with suggestions but to resist responding to motoric suggestions. Subjects received either instructions to use goal-directed fantasies (GDFs) or no facilitative instructions. Sizable individual difference effects were secured. Hypnotizable subjects exhibited more suggestion-related movements and reported greater involuntariness than did low-hypnotizable subjects. With GDF instructions, low- and high-hypnotizable subjects reported equivalent GDF absorption and frequencies. However, hypnotizable subjects exhibited greater responsiveness and reported greater involuntariness than did those low in hypnotizability, even when their GDFs were equivalent. Thus, no support was generated for the hypotheses that sustained, elaborated suggestion-related imagery mediates response to suggestion (Arnold, 1946) or that absorption in suggestions is of particular importance for low-hypnotizable subjects (Zamansky & Clark, 1986). Our finding that measures of response expectancy paralelled responding and reports of nonvolition support the hypothesis that expectancies mediate the relation between imagination, involuntariness, and responding (Kirsch, 1985; Spanos, 1982). Hypnotizable imagining subjects in the study discussed here exhibited greater responsiveness than a comparable sample of subjects did in a previous countersuggestion study (Lynn, Nash, Rhue, Frauman, & Stanley, 1983) in which no attempt was made to foster an association between imagining and involuntary responding in the initial screening session.

Adult↗
PubMed1975

Inhibition and enhancement of Friend leukemia virus by pyran copolymer.

Inhibition or enhancement of Friend leukemia virus disease could be produced by treatment of mice with the immunopotentiator, pyran copolymer. The result depended on the route of inoculation of the drug. Prophylactic administration of the drug i.p. retarded splenomegaly, reduced splenic foci, and increased survival time of mice infected with Friend leukemia virus. Conversely, when the same dose and regimen of pyran was administered i.v., splenomegaly was enhanced, splenic foci were increased, and survival time was decreased. Histopathological examination of the spleens of mice revealed that i.p. pyran administration caused a marked increase in the splenic marginal zone with some increase in erythropoiesis in the red pulp, while i.v. pyran administration did not markedly change the splenic marginal zone but caused an early and sustained increase in erythropoiesis in the red pulp.

Animals↗