Overview

During the 1960s, Tart undertook a systematic investigation into the nature of suggestibility and responsiveness across different mental states. A central question animated this work: Is hypnosis a unique state in which individuals become unusually responsive to suggestions, or can comparable responsiveness be achieved through other means, such as waking imagination? This question was not merely academic, it bore directly on how psychologists should conceptualize hypnosis itself and what mechanisms underlie suggestion effects.

Tart’s approach was grounded in rigorous experimental methodology. Rather than relying on clinical observations or anecdotal reports, he designed controlled laboratory studies that could isolate the effects of different induction procedures while holding other variables constant. His collaboration with Ernest Hilgard, a leading hypnosis researcher at Stanford University, lent additional credibility and scope to the work. Together, they produced findings that challenged the prevailing assumption that hypnosis represented a qualitatively distinct state uniquely conducive to suggestion.

This research program was part of a broader intellectual movement in the 1960s toward more precise, empirical study of consciousness and altered states. Tart was simultaneously developing his theoretical framework for understanding altered states of consciousness (work that would culminate in his influential 1969 anthology) and his experimental investigations of suggestion responsiveness contributed essential data to that larger theoretical project.

Experimental design and methodology

The landmark study conducted by Hilgard and Tart employed a straightforward but powerful design: participants were randomly assigned to receive either a formal hypnotic induction or waking-imagination instructions, and their responsiveness to a standardized set of suggestions was then measured.¹ The waking-imagination condition was not a control condition in the traditional sense; rather, it was an active alternative procedure designed to elicit imaginative engagement without the formal trappings of hypnotic induction.

The suggestions themselves were drawn from established hypnosis assessment scales and covered a range of phenomena: motor suggestions (arm heaviness, hand levitation), sensory suggestions (anesthesia, hallucinations), and cognitive suggestions (amnesia, time distortion). Participants’ responses were objectively recorded and quantified, allowing for statistical comparison between the two conditions.

Critically, Tart and Hilgard recognized that the experimental situation itself (the setting, the experimenter’s demeanor, the participant’s expectations) could influence outcomes. This awareness led them to examine how contextual factors shaped responsiveness patterns. In a follow-up methodological paper, Tart and Hilgard explicitly addressed the problem of implicit assumptions embedded in experimental designs, noting that researchers often failed to recognize how their own framing of conditions could bias results.³

Tart also conducted related investigations into the nature of suggested dreams and dream-like experiences. In one study, he compared dreams suggested during hypnosis with dreams suggested during sleep, examining whether the state in which a suggestion was given influenced the phenomenological character of the resulting dream.⁴ This work extended the investigation of suggestion responsiveness into the domain of sleep and dreaming, revealing state-specific effects.

Implications and interpretation

The findings from Tart’s research on suggestion responsiveness had several important implications. First, they suggested that hypnosis might not be a uniquely powerful state for producing suggestion effects. If waking imagination instructions could elicit comparable responsiveness, then the mechanisms underlying suggestion effects might be more general psychological processes (such as imaginative absorption, motivation, and expectancy) rather than something specific to the hypnotic state itself.

This conclusion did not mean that hypnosis was ineffective or uninteresting; rather, it reframed the question. Instead of asking “What is special about hypnosis?” researchers might ask “What psychological processes facilitate responsiveness to suggestions, and how do different induction procedures activate those processes?” Tart’s work thus contributed to a shift in hypnosis research away from essentialist definitions based on phenomenological lists and toward functional, process-oriented approaches.

Second, the research underscored the importance of experimental design and the experimenter’s role in shaping outcomes. Tart was acutely aware that the implicit assumptions built into research procedures, how conditions were labeled, what participants were told to expect, how the experimenter presented the task, could significantly influence results.² This sensitivity to the social and contextual dimensions of laboratory research was ahead of its time and foreshadowed later developments in the psychology of experimenter effects and demand characteristics.

Third, Tart’s comparative studies of suggestion effects across different states (waking imagination, hypnosis, sleep) contributed to a more nuanced understanding of consciousness itself. Rather than viewing consciousness as a simple binary (awake or asleep, hypnotized or not), his work suggested that consciousness comprises multiple subsystems and dimensions that could be independently modulated. This insight would later become central to his systems theory of altered states of consciousness.

Methodological considerations and refinements

In reflecting on his own research, Tart demonstrated a commendable willingness to examine and critique his own methodological assumptions. Years later, in a commentary on hypnosis research, he acknowledged that even he had initially accepted without sufficient scrutiny the conventional definitions of hypnosis based on lists of phenomena.⁵ This intellectual honesty, the recognition that authorities and established frameworks could embody unexamined cultural and conceptual biases, became a hallmark of his approach to consciousness research.

Tart recognized that the way hypnosis was defined and studied in mainstream psychology often excluded or minimized phenomena that did not fit conventional materialist assumptions. For instance, potential parapsychological aspects of hypnosis were systematically omitted from standard lists of hypnotic phenomena, not because they had been disproven, but because they were deemed theoretically inconvenient.⁵ This observation led him to advocate for more open-minded, empirically grounded approaches to consciousness research that did not prejudge what phenomena were possible.

The methodological rigor Tart brought to the study of suggestion responsiveness, careful control of conditions, objective measurement, awareness of experimenter effects and contextual influences, became a model for his later work in parapsychology and transpersonal psychology. He consistently argued that rigorous methodology and openness to unexpected findings were not incompatible; indeed, they were mutually reinforcing.

Broader significance for consciousness research

Tart’s research on suggestion responsiveness contributed to a broader reconceptualization of hypnosis and altered states in the 1960s and beyond. By demonstrating that suggestion effects were not unique to formal hypnotic induction, he helped shift the field away from viewing hypnosis as a mysterious or quasi-magical state and toward understanding it as involving ordinary psychological processes (imagination, attention, expectancy, and motivation) that could be engaged through various procedures.

This reframing had important implications for how researchers approached the study of altered states more generally. If hypnosis was not a unique state but rather a particular way of organizing and directing consciousness, then other altered states (meditation, dreaming, psychedelic experiences) might similarly be understood in terms of how they reorganized consciousness rather than in terms of some essential quality that made them fundamentally different from ordinary waking consciousness.

Tart’s work also highlighted the importance of subjective report and phenomenological investigation in consciousness research. While he valued objective measurement, he recognized that understanding consciousness required attending carefully to how people experienced and described their mental states. This commitment to bridging subjective and objective approaches became increasingly important as he developed his systems theory of altered states and his later work in parapsychology and transpersonal psychology.

Furthermore, Tart’s sensitivity to the role of the experimental situation and the experimenter’s implicit assumptions anticipated later developments in the psychology of experimenter effects and the sociology of scientific knowledge. His recognition that researchers’ own cultural assumptions and theoretical commitments could shape their observations and interpretations was a prescient insight that remains relevant to contemporary consciousness research.