Colin MacLeod 2026-10-25
A clinical and cognitive psychologist at the University of Western Australia whose work investigates anxiety-linked information processing. [ref][ref]
Figure 1.
Portrait of Colin MacLeod
. University of Western Australia profile portrait. Source.
Anxiety disorders centrally involve cognition, but describing them solely as disorders of cognition is too strong unless the term is defined so broadly that it loses explanatory value. Threat appraisal, attention, interpretation and memory can contribute to excessive fear and avoidance. Bodily arousal, learning history, action and the environment also matter. A useful account specifies how these processes interact and asks whether changing a proposed cognitive process changes anxiety, rather than simply observing that anxious people report anxious thoughts.
David M. Clark's cognitive model of panic illustrates the explanatory gain. Ordinary sensations such as a racing heart can be interpreted as evidence of imminent catastrophe. Fear increases arousal, which provides further sensations for threatening interpretation. The account distinguishes the bodily input from its meaning and explains why similar sensations need not produce the same fear in different circumstances. It also predicts that precautions and avoidance can prevent disconfirmation. The 1986 paper supplied a mechanistic model, not by itself proof that every panic episode requires a consciously articulated catastrophic thought.[ref]
The distinction between cognition and explicit verbal reasoning matters. A person may orient rapidly toward threat, experience an image or respond to a bodily sensation before they can describe a proposition. Absence of a reported sentence does not establish absence of information processing. Equally, a theory should not rescue itself from every negative finding by postulating an inaccessible belief. It must specify observable predictions and measures that can fail, including what would count as successful alteration of the proposed process.
Cross-sectional evidence is insufficient to establish direction. A threat interpretation could increase anxiety, anxiety could bias the interpretation, or a third factor could influence both. Questionnaires can also partly measure the same evaluative content on both sides of the association. Longitudinal prediction improves temporal ordering but leaves confounding possible. Experiments that manipulate interpretation or attention therefore offer a stronger test, especially when changes in the intended process are verified separately from changes in symptoms.
Andrew Mathews and Bundy Mackintosh reported five experiments inducing relatively threatening or benign interpretations of ambiguous material. Interpretative bias could be changed, but parallel effects on state anxiety depended on active processing of personally relevant meanings. This supports a causal contribution under specified conditions and shows that a changed task response need not automatically mean changed emotional experience. These experiments do not establish that an interpretation-training task is a complete treatment for a diagnosed anxiety disorder.[ref]
Colin MacLeod and colleagues manipulated selective attention using a modified dot-probe procedure. The location of a subsequent probe was used to train attention in different directions relative to emotional material, followed by a standardised stress task. Differences in emotional vulnerability support a contribution from attention rather than association alone. Transfer from a laboratory induction to enduring clinical change, however, remains an additional question. Learning a task contingency, altered expectancies and the reliability of the process measure all require consideration.[ref]
Clinical treatment comparisons provide complementary evidence. David M. Clark and colleagues compared cognitive therapy, applied relaxation and imipramine in panic disorder, with self-exposure homework shared across conditions. The findings supported cognitive therapy as a useful treatment. They do not make the comparison a pure test of thought change against an absence of learning or behavior: treatment packages differ in multiple ways, and a pharmacological treatment can also alter the sensations and experiences from which beliefs are formed.[ref]
Safety behavior research further shows why a sharp cognition-versus-behavior division can mislead. Paul Salkovskis and colleagues found that changing precautions during exposure altered catastrophic beliefs and anxiety. The behavior may control which evidence is encountered and how success is explained. Conversely, a different explanation may make abandoning the behavior possible. These reciprocal effects favour a specified feedback system over treating observable action and mental representation as competing, self-contained causes.[ref]
Learning accounts also need not exclude cognition. An inhibitory learning approach proposes that exposure establishes alternative expectations rather than necessarily erasing the original threat association. Context-dependent retrieval can explain return of fear after apparently successful practice. Michelle G. Craske and colleagues developed a translational framework around this distinction. It offers a way to connect expectation, experience and later retrieval, while its clinical implementation requires direct evaluation rather than assuming that a learning rationale proves a particular protocol optimal.[ref]
The broader phrase 'anxiety disorders' also conceals heterogeneity. The feared consequence in social anxiety differs from the interpretation of bodily sensations in panic or persistent worry about many possible outcomes. A common information processing principle can coexist with disorder-relevant mechanisms. Actual danger and social adversity must be assessed: an expectation is not distorted simply because it concerns something distressing. Genetic, developmental and physiological influences can affect sensitivity to threat without fixing the meaning or outcome of every encounter.
Strong evidence for a particular cognitive mechanism would combine an experimental manipulation, a successful process check, subsequent change in fear and transfer to relevant everyday behavior. A factorial design could vary interpretation and a maintaining precaution separately, with matched contact and exposure opportunities. Repeated measurements should establish whether the cognitive change precedes the outcome. Treatment randomisation identifies the package effect, but mediation requires additional assumptions because the mediator itself has not necessarily been randomised.
Evidence against an exclusive account would include effective treatment without the predicted process change, or a precise null effect on anxiety after a successful, sufficiently strong manipulation of that process. Such a result might constrain the population or context in which the mechanism matters rather than rule out all cognitive contributions. Measurement sensitivity and alternative pathways must be considered without making the theory unfalsifiable.
The defensible conclusion is that cognition contributes materially to the persistence and modification of anxiety, with experimental evidence beyond introspective report. It is less defensible to claim that all anxiety disorders are caused only by consciously held false beliefs, or that the success of cognitive therapy establishes that exclusivity. Mechanistic precision and evidence about causal interaction are more informative than choosing between cognition, the body and behavior as if only one could matter.
A psychological treatment has a specific effect only relative to a clearly defined alternative explanation. Benefit beyond waiting is different from benefit beyond credible therapeutic contact, and both differ from evidence that a named technique works through its proposed mechanism. No single research design establishes all three. A persuasive programme combines controlled clinical comparisons with component and process experiments, while keeping patient-relevant outcomes central.
An uncontrolled before-and-after study cannot isolate a treatment effect. People may enter care when symptoms are unusually severe, creating regression toward their longer-term level; difficulties can improve naturally; expectations, concurrent care and repeated assessment can also change outcomes. A waiting-list randomised trial controls some time-related explanations but adds unequal expectations and contact. It can establish benefit from being offered the treatment package compared with waiting under those conditions, without identifying which ingredient produced the difference.
For specificity beyond nonspecific therapy effects, use a randomised comparison with a credible active intervention. Match time, attention, therapist competence and assessment opportunities as far as the question permits. Measure credibility and expected benefit rather than assuming equivalence from similar session counts. Keep relevant usual care available in both arms. Allocation concealment prevents recruitment decisions from anticipating the next assignment, while blinded independent outcome assessment reduces a different source of bias after allocation. Therapists and patients usually cannot be fully blinded to psychological procedures.
Daniel Freeman and colleagues' Feeling Safe trial illustrates this stronger package comparison. Patients with persistent persecutory delusions received the programme or befriending delivered by the same therapists, alongside usual care. At six months, the primary continuous conviction measure favoured Feeling Safe. This supports an effect beyond the particular befriending comparator, but does not establish that each module is necessary or that the whole benefit travelled through one nominated mediator.[ref]
The comparator should be interpreted fairly. A weak or implausible control can exaggerate apparent specificity, while an active comparator may itself change the proposed mechanism. If befriending improves social confidence, it is not a biologically inert placebo. A null result may mean two useful treatments have similar effects, both are ineffective, or the study is too imprecise. Failure of a superiority test does not demonstrate equivalence; an equivalence or noninferiority question requires prespecified clinically justified margins and appropriate precision.
A dismantling trial varies a specified component while keeping the surrounding treatment adequate and similar. For example, compare the same exposure programme with and without a safety behavior intervention. This estimates a conditional contribution: absence of an additional benefit does not imply that the component is useless in every context, because another part may produce similar learning. A factorial design can independently vary an action and its explanatory rationale, estimating their effects and interaction when the study has adequate power.
The early panic safety behavior experiment provides both an example and a caution. Greater change after brief exposure with precautions reduced supports the combined manipulation. Yet behavioral instructions and the explanation of the exercise were not fully separated. The appropriate next test would vary those elements independently and check actual behavior and expectancy change. Simply renaming the conditions 'cognitive' and 'behavioral' would not remove the confounding.[ref]
A mechanistic experiment can provide more direct leverage than a full treatment comparison. Colin MacLeod and colleagues trained attentional bias using a modified dot-probe task and tested later responses to stress. This asked whether experimentally changing information processing altered emotional vulnerability. It remains necessary to establish that the manipulation engaged the intended process rather than only a task-specific strategy, and that any effect transfers to the clinical phenomenon of interest. Laboratory emotional vulnerability is not itself diagnostic remission.[ref]
Likewise, Daniel Freeman and colleagues used virtual social environments to compare exposure against threat testing with safety behavior reduction. Both groups encountered graded situations, making the content of learning more directly investigable than in a therapy-versus-waiting comparison. The combined manipulation and brief follow-up constrain the mechanism claim. A useful manipulation check, an independent behavioral outcome and later transfer assessment strengthen the design more than a treatment label does.[ref]
Mediation analysis is informative but insufficient on its own. Randomising treatment identifies the total effect of assignment under the trial's assumptions; it does not automatically randomise the mediator. Symptom improvement could change reported beliefs, or an unmeasured process could influence both the belief score and the outcome. Measure the proposed mediator before the downstream outcome, assess competing pathways and perform sensitivity analyses. Replication using a different way to alter the same process can provide converging evidence; stronger identification may require experimental manipulation of that process itself.
Clinical trials also need suitable sampling, prespecified outcomes, adequate power, intention-to-treat analysis and transparent missing data handling. Outcomes should include functioning and possible deterioration, with follow-up long enough to distinguish transient reassurance from durable benefit. Treatment fidelity and competence must be assessed in both arms. Therapist allegiance, clustering of patients within therapists and differential dropout can affect interpretation. Statistical significance alone does not establish a meaningful improvement, especially when many outcomes or subgroup comparisons are explored.
Pragmatic implementation trials answer a complementary question: does the intervention add benefit in ordinary care, at acceptable cost and burden? Jaime Delgadillo and colleagues' therapist-cluster trial tested an automated feedback system linked to supervisory review within routine services. Its comparison isolates the added feedback arrangement more closely than an observational association between high-performing services and monitoring. It still tests a specified package of information and response, rather than an abstract effect of measurement divorced from clinical action.[ref]
The strongest conclusion consequently states its level of specificity. A well-conducted active control trial can establish an incremental treatment-package effect. A dismantling or factorial trial can identify a component's contribution within a defined context. An experimental process manipulation, supported by temporally ordered measurements and converging clinical evidence, can constrain the mechanism. Keeping these claims separate prevents a successful therapy from being treated as proof of its entire theory, while preserving the practical importance of improvements patients actually experience.