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Lorenz's Hydraulic Model of Motivation


We know from everyday experience that the more motivatedwe are, the more responsive we are to stimuli in our environment. For example, if I am very hungry I am more likely to eat something that I am not particularly fond of, just to satisfy my hunger.

This page explains several important theoretical ideas from classical ethology:

  • Lorenz's Hydraulic Model
  • fixed action patterns
  • action specific energy
  • vacuum activities
  • The Innate Releasing Mechanism
  • Behavioural quiescence
  • Lorenz's Hydraulic Model of Motivation

    Lorenz' model describes the relationship between:

  • behaviour (fixed action patterns)
  • motivation (action specific energy)
  • external stimuli (sign or releasing stimuli)
  • This animation is based on the type of (static) diagram used in many textbooks to explain Lorenz' model

    Konrad Lorenz developed a model that brings together the main ideas of classical ethology to explain animal motivation.

    It should be emphasized that this is a model, it does not pretend to be an accurate picture of structures that actually exist within the brain. Instead it is a way of visualizing how various hypothetical systems work together to organize an animal's response to its internal and external environment.

    It is called a hydraulic model because it views motivation as a liquid whose accumulation and discharge influences behaviour. consequently some people call it 'Lorenz's water closet'

    Action specific energy (motivational energy) accumulates in a reservoir until released by an appropriate sign stimulus, represented by weights on a scale pan, or until the pressure on the valve causes an action pattern to occur spontaneously (vacuum activity).

    The consummatory response or Fixed Action Pattern(s) released vary depending upon how much action specific energy is released from the valve.

    Points to ponder:
  • What is the effect of the passage of time on the act that will be performed when a specific weight is placed on the pan?
  • What act will be performed if a heavy weight is placed on the scale pan very shortly after a very heavy weight was placed on the scale pan?
  • Fixed action patterns(FAPs)

    FAPs are relatively stereotyped behaviours(i.e. they seem to run like clockwork) exhibited by all members of a species under appropriate conditions.

    FAPs are normally seen when an animal in an appropriate motivational state is exposed to the appropriate external stimulus - this stimulus was called a releaser or sign stimulusby ethologists.

    A collection of FAPs is called an ethogram.

    Action specific energy

    In Lorenz's model motivation increases with the passage of time. This motivation is specific for one type of behaviour (e.g. either feeding, or fighting or sexual behaviour). This specific source of motivational energy is called action specific energy. It is represented by the accumulation of water in the blue reservoir. The reservoir is filled by a tap.

    Points to ponder:

  • Is this an over-simplification?
  • How - and why - would you improve the model to be a more accurate representation of Lorenz' ideas?
  • Lorenz postulated that the reservoir was being continuousy filled with water in order to expain a phenomenon which he called vacuum activity

    Vacuum activity

    Lorenz coined the term vacuum activity to describe behaviour which apparently occurs in the absence of any external stimulus. In the hydraulic model, action specific energy can accumulate to such a high level that the pressure of water in the reservoir is capable of pushing open the restraining valve. This causes water to flow into the trough, and out through holes in the floor that represent fixed action patterns.

    The Innate Releasing Mechanism

    Lorenz introduced the term innate releasing mechanism (IRM) to describe a central ( located somewhere in the brain) mechanism that handled the link between external stimulus, internal motivation and behavioural output. The scale pan, pulley, trough and outflow pipes in the model correspond to the IRM.

    Behavioural quiescence

    An important feature of the model is that after the animal has engaged in a particular behaviour (FAP) there is a period of time when they less likely to respond even if the same stimulus is presented again - behavioural quiescence.
    This occurs because the reservoir has been drained of action specific energy.

    Limitations of Lorenz's Hydraulic Model

    Models and theortetical systems are useful because they organise research findings and suggest further experiments. Models often help reveal the principles underlying the organisation of behaviour. But they do not necessarily tell us much about the actual brain mechanisms involved.

    Clearly the brain does not operate like a toilet - except in some special circumstances! One of the most powerful criticisms of Lorenz's model is that it does not include any mechanism for learning. There is no way that the consequences of the animal's behaviour can feedback into the system to influence subsequent behaviour.

    Lorenz saw no need for it to include feedback. After all he was interested in FAPs - behaviours which by definition do not change over an animal's lifetime. We now know that FAPs do not always spring fully-formed into the animal's behaviour. FAPs are subject to modification during development.

    But this is not a criticism of Lorenz, rather it is an illustration of how Lorenz's ideas led to greater understanding. You have got to start somewhere, and the journey will be a lot easier if the first steps are taken by someone of Lorenz's stature.

    Lorenz was not blind to the crude nature of his theoretical model.

    In 1950 he wrote:

    "This contraption is, of course, still a very crude simplification of the real processes it is symbolizing, but experience has taught us that even the crudest simplisms often prove a valuable stimulus to investigation."

    Nevertheless the model has now fallen out of favour because it proved impossible to locate structures in the brain where action specific energyaccumulated within a reservoir or processes that functioned like the postulated IRM.

    So what now? .....

    Students often ask "So what has this got to do with human behaviour?"
    One answer is that Lorenz's model of motivation has been used as an explanation of human aggression. You will recall from from an earlier sectionthat:

    "In Lorenz's model motivation increases with the passage of time. This motivation is specific for one type of behaviour (e.g. either feeding, or fighting or sexual behaviour). This specific source of motivational energy is called action specific energy. It is represented by the accumulation of water in the blue reservoir. "

    According to this view the only way to reduce human aggression is to engage in aggressive behaviour. Furthermore there will come a time - according to the model - when aggressive behaviour will be exhibited in the absence of any provoking stimuli, so called vacuum activity.

    You might wonder if this view was seriously held. Yes it was. In 1963 Lorenz published a book "On Aggression". It was republished in 1996 by Rouledge with a special introduction by Eric Salzen which is well worth reading. Salzen describes how the controversy raised by Lorenz's ideas culminated in 1986 when UNESCO and the American Psychological Association published a statement which was intended to:

    ".. dispel the widespread belief that human beings are inevitably disposed to war as a result of innate, biologically determined aggressive traits"

    A note to instructors

    You may wonder why I have based this teaching resource on such a heavily criticised set of concepts and theoretical model. The answer is that - from a teaching point of view - they provide fertile ground. This resource was designed for use with first year psychology undergraduates as part of module taught by a small team of lecturers who present views on a single topic from different perspectives (biological, behaviourist, cognitive etc.)

    My aim is to gently expose students to:

  • identifying and recording behaviour
  • a simple, easily grasped theory
  • a critical appreciation of an intellectual heritage
  • begin to develop critical faculties
  • begin to appreciate the problems of animal to human extrapolation
  • At first I expect students to be confused by what is going on. That is an intentional part of my strategy. I want students to begin to appreciate behavioural complexity and the problems of observation.