Systematic Desensitisation

Behavioural Treatments for Phobias: Systematic Desensitisation and Flooding

The behavioural approach to treating phobias follows directly from the two-process model: if phobias are acquired through classical conditioning and maintained through the negative reinforcement of avoidance, then treatment should involve exposing the phobic individual to the feared stimulus whilst preventing the avoidance that maintains the fear. This allows the conditioned fear response to extinguish — the CS (feared stimulus) is repeatedly presented without the UCS (original aversive event), and the conditioned association weakens. Two main behavioural treatments are used: systematic desensitisation and flooding.

Systematic Desensitisation

Systematic desensitisation (SD), developed by Joseph Wolpe (1958), treats phobias gradually. The central principle is reciprocal inhibition: anxiety and relaxation are physiologically incompatible — a person cannot be simultaneously anxious and deeply relaxed. By pairing a relaxation response with the feared stimulus at each step of an anxiety hierarchy, the therapist progressively replaces the fear response with a relaxation response.

SD involves three stages. First, the therapist teaches the client a technique for achieving deep relaxation — typically progressive muscle relaxation or controlled breathing — which the client practises until proficient. Second, therapist and client collaboratively construct an anxiety hierarchy: a ranked list of situations involving the phobic stimulus, from least to most anxiety-provoking, typically rated using Subjective Units of Distress Scale (SUDS, 0–100).

Third, the client works through the hierarchy, beginning at the lowest step. They are exposed to the stimulus at that level whilst maintaining relaxation. Once they can remain relaxed during exposure at one level, they progress to the next. This continues until the client can tolerate the most anxiety-provoking step without significant distress. Exposure can be conducted in vitro (through imagination) or in vivo (through real exposure to the feared stimulus), with in vivo exposure generally more effective.

Flooding

Flooding (also called implosion therapy or prolonged exposure) takes a radically different approach. Rather than gradual exposure, the client is exposed immediately and intensely to the most feared version of the stimulus — at the top of the anxiety hierarchy — and is prevented from escaping or avoiding. The rationale is straightforward: anxiety cannot continue indefinitely. The autonomic nervous system naturally reduces arousal if the threatening stimulus is maintained but no actual harm results. If the client remains in the feared situation long enough, the fear response extinguishes because the UCS (original aversive event) does not occur — the CS (feared stimulus) is presented without consequence until the conditioned response diminishes.

Flooding is typically faster than SD — sometimes a single extended session can produce significant reduction in phobic fear. However, it is an intensely distressing experience for the client and requires full, informed consent and psychological preparation. There is also a risk of symptom return or sensitisation if the session is not maintained long enough for full extinction to occur.

Evaluation

Both SD and flooding have strong empirical support. Meta-analyses (e.g. Wolpe, 1958; more recently, Craske, 2015) confirm that behavioural exposure treatments are highly effective for specific phobias, with response rates typically above 80%. SD is more widely used in clinical practice due to its graduated nature and lower distress, and is particularly effective for simple specific phobias. Flooding is faster but more distressing, and is less suitable for clients who cannot tolerate high levels of acute anxiety. Both treatments have limitations for complex phobias: they address the conditioning-based fear response but may not address cognitive distortions (addressed more directly in CBT) or the biological predispositions that made conditioning occur in the first place.