A study was undertaken of long-term meditators within the Sahaj Marg Raj Yoga practice to investigate how change was perceived through time and how this altered constructs of self and interpersonal behaviour. Comparisons were made with psychotherapists in training as a control group involved in personal and attentional development procedures. The study used qualitative, quantitative and experimental methodology. Semi-structured interviews were carried out with 31 meditators who had been meditating for an average of 16 years. Using Grounded Theory Analysis, thematic content was constructed into a hypothetical theory of the process of change. A similar qualitative method was applied with a small group of psychotherapists. The overall core theme of 'deepening search' described the processes of change and was compared with Wilber's theories of development. Some of Quekelberghe's scales for Altered States of Consciousness were applied to 61 meditators and 67 psychotherapists: comparisons were made with scales relating to positive mystical states, life change, hypersensitivity, dreams and changes in experience of body, space and time, and a specially devised scale to measure changes in perception and empathy. Significantly higher scores were obtained for meditators than psychotherapists for Positive Mystical Experience, Change and Subtle Perception. Based on an experimental study by Brown, Forte and Engler, a series of abstract watercolours was used as a perceptual cue and responses from 9 meditators and 9 psychotherapists were analysed. Significantly higher scores were found for the meditators in categories related to an increase of phenomenal aspects of perception. The results of the three studies taken together suggested that affective experiences were more significant than attentional development in contributing to changes in self-construct and interpersonal behaviour. The finding was discussed in relation to current theories of Wilber and Damasio.