Some Short Notes From a Long Career


Dear blog reader,

It is with great pleasure that we welcome Professor Julian Leslie to the series. Julian’s contribution to behavior analysis in Ireland, the UK, and indeed the whole of Europe, cannot be underestimated. As you will see from Julian’s blog, his academic lineage can be traced back to some of the most prominent and influential figures in behavioral analysis and psychology generally. Despite this lineage and his own contribution to the field, he remains forever humble. Julian has always been extremely generous with his time and is completely devoted to teaching and nurturing students, and also more junior academics and researchers. Indeed, Julian was Dermot’s undergraduate mentor and joint PhD supervisor and has remained a constant source of support and inspiration throughout Dermot’s career. One feature that marks Julian out as a behavior analyst has been his ongoing efforts to explore ways in which behavior analysis can synergise with areas outside of the field. As such, his blog is an ideal example of the cooperative and collaborative theme that we wish to promote with this series. We are sure that you will enjoy reading Julian’s contribution and hope that you see it as a narrative that will serve to reinforce ongoing efforts to find common ground both within and outside of behavior analysis.

Dermot and Colin

About the author:

Julian Leslie is a professor in the School of Psychology at Ulster University. He holds a DPhil in experimental psychology from Oxford University and a DSc in the experimental analysis of behaviour from Ulster University. He is a Fellow of the Association of Behavior Analysis International. As well as the strands of research mentioned here, he has written several textbooks on behavior analysis, and published extensively in behavior pharmacology and behavioral neuroscience. In the 1970’s, he was co-founder of Behaviour Analysis in Ireland and has supervised more than 50 PhD students over the course of his career to date.

Some Short Notes from a Long Career

Archives nationales, Public domain, via Wikimedia Commons

Genealogy is very popular, at least as a hobby, and we all have a general idea as to why it is important. Academic (or intellectual) genealogy is a more obscure topic, but one method involves tracing the “lineage” of those who have obtained doctorates back through successive generations of supervisors or mentors. The rules for this are more arbitrary (see Roediger, 2005, for a brief discussion) but it is easy to get started, and there are now several publicly available databases. It is fun to do, but also very revealing – you can use it to trace the development of major strands of a discipline. This isn’t surprising; PhD students typically begin work in an intellectual and methodological framework set by their supervisor’s current views and activities. Relatedly, we know that early experience is very important. This is much harder to track but we would expect to find that the range of interests or topics developed by an individual researcher would likely reflect courses they took early on, i.e., while an undergraduate or Masters student.

So what? Well, I was invited by Colin and Dermot to write something about my diverse career in pursuit of their objective of breaking down barriers between the silos that have developed in behavior analysis. I very much support that, and I have personally been trying, however feebly, to make links with other disciplines that share our commitment to versions of environmentalism and reject “representationalism”. Those links are hard to establish, a point that I will come back to, but it will help enormously if it is clear that within behavior analysis we all share some key principles. This was well-put by Colin and Dermot in their position statement, “In our view, we are too small a field to divide ourselves into even smaller sub-groups, and from what we can see there is indeed tremendous overlap in the research that we are all doing, even if we often use different terms and concepts to talk about the behavior we are studying. Critically, we all seem to be aiming to develop a behavior-analytic, monistic, and naturalistic account of human language and thought that is devoid of mentalistic theorizing and speaks directly to practical concerns in educational, clinical, organizational, and other settings” (Harte & Barnes-Holmes, 2021).

Julian in 1978

My first degree was in Psychology and Philosophy at Oxford University. This meant that it was in experimental psychology (including some animal behaviour) and “Oxford philosophy” which at that time (the late 1960’s) was strongly influenced by ordinary language philosophy.  Exposure to these influences might reasonably lead to an interest in behaviorism and behavior analysis. However, that wasn’t very likely in practice because of a large countervailing factor: the high level of hostility in British academia to the work of B.F. Skinner. My case was unusual (just as everyone’s case is unusual), in that I took a course of tutorials and then did a research project in my final year with Jock Millenson. Jock was a Columbia University PhD, where he was mentored by W. N. Schoenfeld, he published repeatedly in JEAB and had already published his undergraduate text, Principles of behavioral analysis (1967).  Jock stayed in Oxford long enough for me to start a PhD research program in the operant lab he had established, but he then left and my PhD supervision was taken over by Jeffrey Gray. Jeffrey contributed hugely in a range of areas of biopsychology, including the neuropsychology of anxiety, a theory of the biological basis of personality, and, lastly, a book about consciousness. Perhaps testament to the influence of early experience over later ones, I remained stoically interested in operant conditioning and behavioral (rather than neurological) explanations, although working with Jock I had also developed a parallel interest in behavioral pharmacology which has persisted.

In the 1970’s,  a large majority of behavior analysts were working in operant conditioning labs (with non-human animals) with some of them moving from there into behavior pharmacology labs. At the time, I think I saw the vast – but remote- field of human language and cognition as a challenge that we would come to in due course, but I wasn’t at all sure how we would move from where we were (in my case engaging in the molecular versus molar explanation debate as it applied to rat operant behavior) to the point where we could offer a behavioral account of everyday human language. Fortunately, that other Columbia PhD, Murray Sidman (also mentored by W. N. Schoenfeld), had already begun to cross the divide. I could have known that in the 1970’s but didn’t read the right papers. Instead, I did take an excursion into attempts to provide behavioral account of everyday human language with a different methodology. With a PhD student, Sabrina Halliday, we devised a naturalistic study of language acquisition in young children. Mother–child dyads were videotaped during fortnightly 30-minute sessions. At the outset, the children were aged 9-29 months and they took part in the study for more than 6 months. Using a coding system, we looked for common patterns of mother–child interactions. Certain patterns were found to be used across the entire age range, whilst others were used only at particular ages. The majority of the more stable patterns of interaction involved imitation by the mother or child, or both, and the child’s non-verbal compliance with the mother’s instructions. There were interesting changes with age as well. I thought that the developmental psychology community would be excited by these findings, but they were not in tune with the post-Chomsky zeitgeist. They took a long time to publish (Halliday & Leslie, 1986), and have not often been cited.

While that strand of research didn’t continue, I did return to the general area of language and cognition once I was fully conversant with the impact of Sidman’s ground-breaking studies of stimulus equivalence. My eventual contributions reached across areas to some extent, rather than staying within the developing silo of stimulus equivalence research. In one study, we used a conventional stimulus equivalence training procedure with words denoting threatening situations as “A” stimuli, nonsense syllables as “B” stimuli and pleasant state adjectives as “C” stimuli. Non-anxious participants mostly passed subsequent C-A tests for equivalence, but clinically anxious participants did not. The paper (Leslie et al., 1993) has been quite widely cited, but an informal inspection of the titles of 100 publications that cite it show them virtually all to be authored by behavior analysts, broadly defined, even though we suggest in the paper that the striking findings could lead to straightforward application in clinical screening for anxiety.

Another study was done with a colleague whose earlier training was in the cognitive psychology of olfactory learning and involved stimulus equivalence classes involving olfactory stimuli. Adults were to match odor stimuli (smells) with nonsense syllables (A-B training). This turned out to be a hard task, but if they met a criterion of successful performance, they were then trained to match the nonsense syllables to line drawings (B-C training). Following successful performance on that, there was a C-A test phase. 13 out of 14 participants who reached  the C-A test trials achieved at least  97% success, showing stimulus equivalence class formation where one element of each stimulus class was an olfactory stimulus. There are fewer citations of this paper (Annett & Leslie, 1995), but inspection of 50 citing titles shows only one that is clearly in the (cognitive) olfactory memory literature.

Photo by monicore:

Subsequent work includes one unusual applied study where we observed directly that customers in a large retail store don’t go out through the emergency exits when there is an unannounced building evacuation (i.e., when the building occupants don’t know that there isn’t really an emergency). Instead, they tend to leave the way they came in. We speculated that stimulus equivalence led them to treat the labelled exits as locations to avoid rather than approach. This paper (McClintock et al., 2000) has been cited in the fire technology literature, but I don’t know whether it sparked an interest in equivalence research.  A more recent study evaluated the application of equivalence-based instruction to teach categorization of real-world stimuli from non-overlapping categories (e.g., toys, clothing, and fruit). Typically developing preschool-age children (aged around 4 years) were trained in six conditional discriminations, tested for the emergence of three three-member classes, and then trained to identify receptively the category label for one stimulus in each class. Following training, all participants demonstrated categorization of the directly trained class members and further generalization to additional untrained stimuli (Barron et al., 2018).

I have grumpily mentioned several times that research I have been involved in often makes contact with other research areas and approaches but hindsight, through examining citations, indicates that behavioral research by me and colleagues, at least, is not often picked up by researchers from those areas. This de facto isolation is often commented on by behavior analysts, and some scholarly analyses (e.g., Morris, 2014) have laid out the ways in behavior-analytic research can be made more accessible to those in other disciplines. Another straightforward explanation as to why even my more cited papers stay inside the field or silo of behavior analysis is that they are not interesting enough! Examining the citations of one of Dermot Barnes-Holmes’s highly cited IRAP papers (Barnes-Holmes et al. 2006), shows that one-third of the 40 most recent citations are clearly outside the field in publications classified as social psychology, cognitive psychology, applied psychology etc. Even more impressively, my favourite book by behavior analysts, Meaningful differences in the everyday experience of young American children (Hart & Risley, 1995) has been cited more than 11000 times over 25 years, and is still getting around 500 citations a year, mostly in the areas of educational and developmental psychology.

So, it is possible to reach those outside the silo, whether that is a small silo within behavior analysis or the larger one that encompasses all behaviour analysts. Some factors have been mentioned, and I will suggest another below. I started off talking about academic genealogy.  In my own case, I committed myself to operant psychology, influenced by philosophy in the tradition of Gilbert Ryle and a brilliant exponent of behavior analysis (Millenson, 1967), even though I was working with Jeffrey Gray a distinguished scientist who would now be called a cognitive neuroscientist (or perhaps a behavioral cognitive neuroscientist). I didn’t change tack (or silos) because I wasn’t convinced that cognitivism, with or without a neurological dimension, made intellectual sense. Jeffrey Gray is perhaps best remembered now for his book on consciousness, sadly published posthumously (Gray, 2004). That book is a tour de force; he reviews a huge amount of experimental literature in pursuit of that holy grail, the neural basis of consciousness. Reading the book reinforced my view of the futility of that pursuit, but made me think I should do some more modest research myself and examine the behavioural account of consciousness. A paper of mine on this topic appeared some time ago (Leslie, 2015) and reviewed some philosophical and empirical issues. My conclusions were perhaps too general; “more research needed”, but I did rather grudgingly concede that some of the research on relational frame theory seemed to be going in the right direction, and that is much more evident in 2022.

Following on from that, and reflecting my early training in the empiricist philosophical tradition, I tried to examine the most basis philosophical underpinnings of behavior analysis. In my paper on this (Leslie, 2021), I concluded that while Skinner’s pragmatism rejects and avoids dualism, there are assumptions in science more generally that may result in us slipping back into dualism. We can avoid this, but to do so we need to be clear on our underlying metaphysical assumptions. The paper is probably not an “easy read”; although I tried to keep it simple, examining different philosophical positions is hard.

RomanDeckert, CC BY-SA 4.0, via Wikimedia Commons

Science makes progress incrementally through the work of scientists, and some of the increments are bigger than others. In my case, the apple probably didn’t fall far from the tree, but during my professional career there have been huge developments in behavior analysis and of course in many allied disciplines. Going forward, I hope we can provide behavior analysts with the capacity to do conceptual analyses that sustain our approach and the motivation to do useful research and integrate it with developments in many of those allied sciences.


Annett,  J.M.  & Leslie, J.  C.  (1995).   Stimulus  equivalence classes  involving olfactory stimuli.  Psychological Record, 45, 439-450.

Barnes-Holmes, D., Barnes-Holmes, Y., Power, P., Hayden, E., Milne, R., & Stewart, I. (2006). Do you really know what you believe? Developing the Implicit Relational Assessment Procedure (IRAP) as a direct measure of implicit beliefs. The Irish Psychologist, 32, 169-177.

Barron, R., Leslie, J.C., & Smyth, S. (2018).  Teaching real world categories using touchscreen equivalence-based instruction. Psychological Record. 68, 89–101.

Gray, J. A. (2004). Consciousness: Creeping up on the hard problem. Oxford University Press.

Halliday, S. & Leslie, J.C. (1986).  A longitudinal study of  the development  of  mother-child interaction.   British Journal  of Developmental Psychology, 4, 211-222.

Hart, B., & Risley, T. R. (1995). Meaningful differences in the everyday experience of young American children. Paul H Brookes Publishing.

Harte, C. & Barnes-Holmes, D. (2021). Escaping our research silos in rising to the challenge of human psychology. [Blog Post].

Leslie, J.C. (2015). Consciousness from the standpoint of behaviour analysis. European Journal of Behavior Analysis, 16, 147-162.

Leslie, J.C. (2021).  The relevance of metaphysics to behavior analysis. Perspectives on Behavior Science, 44, 29-40.

Leslie, J.C., Tierney, K.J., Robinson, C.P., Keenan, M., Watt, A. & Barnes, D. (1993).  Differences between clinically anxious  and non-anxious  subjects  in a stimulus  equivalence  training  task involving threat words.  Psychological Record, 43, 153-161.

McClintock, T., Shields, T. J.,  Rutland, T. R., &  Leslie, J. (2000). Dishabituation and stimulus equivalence could make all emergency fire exits familiar. Journal of Applied Fire Science, 9, 125-134.

Millenson, J. R. (1967). Principles of behavioral analysis. Macmillan.

Morris, E. K. (2014). Stop preaching to the choir, publish outside the box: a discussion. The Behavior Analyst, 37, 87-94.

Roediger, H.L. (2005). Intellectual genealogy.