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.

Event-related markers of unconscious processes.

A series of studies is reviewed strongly suggesting that event-related potentials (ERPs) may provide markers for unconscious processes. In one study it was shown that, although smaller in amplitude by a least a factor of four, ERPs to subliminal stimuli have a similar component structure to ERPs to supraliminal stimuli. In another study, it was shown that an oddball P300 could be obtained for subliminal stimuli. In two additional studies, it was shown that aversive conditioning could be established unconsciously. The implications for our understanding of the role of unconscious processes in phobias and post-traumatic stress disorders are discussed, as well as more general implications for memory formation.

Event-related brain potentials differentiate positive and negative mood adjectives during both supraliminal and subliminal visual processing.

This experiment provides brain event-related potential (ERP) evidence for differential processing of visually presented pleasant and unpleasant affectively valent words (mood adjectives) for both supraliminal (40 ms) and subliminal (unmasked, 1 ms) stimulus durations. Unpleasant words elicited a more positive amplitude than pleasant words in both durations. ERP components (P1, N1, P2, P3, and a late positive potential; LP) were measured at six electrode sites (F3, F4, P3, P4, CzPz, Oz). ERPs to subliminal stimuli demonstrated differences between pleasant and unpleasant words in the left hemisphere across all measured components. Supraliminal processing showed similar differences in the left hemisphere for early components (P1 and N1), but bilateral differences for late components (P3 and LP). Activity in the P2 time window was associated with the divergence between supraliminal and subliminal affective responses. Implications for the study of affect and consciousness are discussed.

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.

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.

Further evidence for unconscious learning: preliminary support for the conditioning of facial EMG to subliminal stimuli.

This study investigated the predictive validity of facial electromyograms (EMGs) in a subliminal conditioning paradigm. Two schematic faces (pleasant; CS- and unpleasant; CS+), were presented to eight right-handed males during supraliminal pre- and postconditioning phases. Subliminal conditioning consisted of 36 energy-masked presentations of each face pairing the CS+ with an aversive shock 800 ms poststimulus. A forced-choice recognition task established that the energy mask effectively precluded conscious recognition of stimuli. For the obicularis oculi and corrugator EMGs, significant face x condition interactions were found at 20-100 ms and 400-792 ms poststimulus. The results demonstrate the existence of an expressive motoric response related to affect operating in response to a learned but unconscious event. Subjects were not aware of a contingency between the CS+ and the US, suggesting emotional contingencies can be unconsciously acquired.

Psychoanalysis as the patient: high in feeling, low in energy.

This paper examines the increasingly important role that affect is assuming in psychoanalytic research and practice. This rise in the centrality of affect has been at the expense of an independent role for motivation and a dismissal of any energy concept. Difficulties with this affect-first approach are identified and an alternative offered that accords motivation an independent role and accommodates a useful energy concept. Research on esophageal atresia, addiction, and infant suckling are cited in support of this position.

Brain indices of nonconscious associative learning.

Using a classical conditioning technique, this study investigated whether nonconscious associative learning could be indexed by event-related brain activity (ERP). There were three phases. In a preconditioning baseline phase, pleasant and unpleasant facial schematics were presented in awareness (suprathreshold). A conditioning phase followed, in which stimuli were presented outside awareness (subthreshold, via energy masking), with an unpleasant face (CS+) linked to an aversive shock and a pleasant face (CS-) not linked to a shock. The third, postconditioning phase, involved stimulus presentations in awareness (suprathreshold). Evidence for acquisition of a conditional response was sought by comparing suprathreshold pre- and postconditioning phases, as well as in the subthreshold conditioning phase itself. For the pre-postconditioning phase analyses, significant ERP component differences differentiating CS+ and CS- were observed for N1, P2, and especially P3. For the conditioning phase, significant differences were observed in the 100-400 ms. post-stimulus region reflecting a CS+ processing negativity. Brain activity does indeed index the acquisition of a conditional response to subthreshold stimuli. Associative learning can occur outside awareness.

Conscious and nonconscious processes: an ERP index of an anticipatory response in a conditioning paradigm using visually masked stimuli.

This study investigates the nonconscious elicitation of a previously conditioned response by using a differential conditioning paradigm with visually masked affectively valent facial schematics. Electrodermal (skin conductance response [SCR] and brain (event-related potential [ERP]) activity were main dependent measures. Following a preconditioning phase in which subjects viewed energy masked pleasant and unpleasant facial schematics, conditioning with an aversive shock was established to unmasked presentations of an unpleasant face in a partial factorial design. A postconditioning phase of masked presentations, when compared with the preconditioning phase, revealed how the conditional effect within awareness might affect the same stimuli when presented outside awareness. An adaptive staircase technique was used to establish individual threshold levels, which represented a methodological advance over procedures typically used in visual masking research. The results revealed that responses to the CS+ (unpleasant face) changed significantly in predicted directions from preconditioning to postconditioning phase when compared with responses to the CS- (pleasant face). The SCR results systematically replicated recent Ohman, Dimberg, and Esteves (1988) findings, with the pattern of responses resembling a resistance to extinction effect. A new finding emerged for the brain responses. For the CS+, distinct slow wave activity occurred just before the point at which the shock had been delivered in the conditioning phase; no such activity was found for the CS-. This slow wave activity is similar to what has been described by others as an expectancy wave. The results indicate that an anticipatory process, as indexed by different physiological systems, can be elicited entirely outside awareness. Implications are discussed in regard to the nature of conscious and nonconscious processes.

An information flow technique for category related evoked potentials.

We report a technique for studying interactions among many subsystems of a biological system. A general mathematical technique is developed for information flow among various subsystems of a system when two or more classes of stimuli are presented to the system. The technique is validated by various simulation studies and then applied to a brain system. The usefulness of the technique is demonstrated for visual event related potentials (ERP's) obtained from human subjects suffering from phobias. The stimuli are briefly flashed words and phrases. The word classes are pleasant, unpleasant, conscious, and unconscious. The conscious class consists of words known by the patient to relate to the problem, whereas the unconscious class of words consists of words related to deep conflicts which are not recognized by the patient. It is demonstrated that information flow is suppressed under supraliminal presentation of the unconscious class, but is strong under subliminal presentation. The technique has the potential of being an objective indicator of conflictual relationships in these patients. The principle of the technique can be applied to any system in which interactions among subsystems are to be analyzed.

An empirical link between lateral eye movements and lateralized event-related brain potentials.

Much recent research has been devoted to the investigation of lateral eye movements (LEMs) as an indicator of hemispheric activation. Various personality characteristics have been reported to be associated with predominant left and right looking which have been interpreted on the basis of hemispheric specialization; however, this interpretation has been challenged by others. We investigated the relationship between LEMs obtained in a paradigmatic question-asking procedure and event-related potentials (ERPs) in response to a checkerboard stimulus. Subjects were 20 right-handed young adults (11 men, 9 women). We found that left-looking subjects had a greater positive-going occipital ERP amplitude at 90-msec poststimulus on the right side than on the left; the reverse was true for right-looking subjects (F = 11.08, 1/16 df, p < 0.005).

Cerebral lateralization and personality style.

Hysterical and obsessive-compulsive style subjects, as determined by a modified Rorschach test and the Wechslar Adult Intelligence Scale Comprehension subtest, were questioned in a face-to-face format where lateral eye movements were surreptitiously observed. Only right-handed subjects were used. It has been argued that lateral eye movements index immediate hemispheric activation after questions--the first such eye movement being a direction opposite to the putatively activated hemisphere. There was significantly more left-looking among the hysterical subjects than among the obsessive-compulsive style subjects.

Field independence, lateralization and defensive style.

This study investigated the relationship between field independence and defense clustering as measured by the Defense Mechanisms Inventory and lateral eye movements. Subjects had previously been classified either as hysterical or obsessive style by the Rorschach and WAIS Comprehension subtest. Previous findings indicate that these subjects have a preferred direction of lateral eye movement in a questioning format (hysterical style = left; obsessive style = right). This study found no relationship between field independence and defense clustering and lateral eye movements. To the extent that eye gaze indexes hemispheric activation, we conclude that neither field independence nor defense clustering was related to hemispheric lateralization.