Trace conditioning as a test for animal consciousness: a new approach


Trace conditioning involves the pairing of a neutral conditioned stimulus (CS), followed by a short interval with a motivationally significant unconditioned stimulus (UCS). Recently, trace conditioning has been proposed as a test for animal consciousness due to its correlation in humans with subjective report of the CS–UCS connection. We argue that the distractor task in the Clark and Squire (1998) study on trace conditioning has been overlooked. Attentional inhibition played a crucial role in disrupting trace conditioning and awareness of the CS–UCS contingency in the human participants of that study. These results may be understood within the framework of the Temporal Representation Theory that asserts consciousness serves the function of selecting information into a representation of the present moment. While neither sufficient nor necessary, attentional processes are the primary means to select stimuli for consciousness. Consciousness and attention are both needed by an animal capable of flexible behavioral response. Consciousness keeps track of the current situation; attention amplifies task-relevant stimuli and inhibits irrelevant stimuli. In light of these joint functions, we hypothesize that the failure to trace condition under distraction in an organism known to successfully trace condition otherwise can be one of several tests that indicates animal consciousness. Successful trace conditioning is widespread and by itself does not indicate consciousness.

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Fig. 1


  1. 1.

    The experiment used differential conditioning of CS+ tone and CS− white noise. For simplicity of exposition, we will only describe the tone condition.

  2. 2.

    Lovibond and Shanks (2002) for a critical review of this literature as discussed further below.

  3. 3.

    ‘Consciousness’ is a contested term both philosophically and scientifically. While there is not sufficient space to offer a full defense of our usage, we offer both subjective and objective reasons in favor of the view that consciousness represents the present moment. Similarly, ‘representation’ can be used in a variety of ways. As we are using the term, a representation is an item in the brain that stands for another item. For example, a representation of a tree is whatever brain process stands for ‘tree.’ We take the process to be functional rather than computational, and representation need not involve picturing the object represented (Droege 2009, 2021).

  4. 4.

    Thanks to an anonymous reviewer for this reference.


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This article owes a deep debt to the late Victoria Braithwaite, our colleague and friend. Her ground-breaking scholarship in animal behavior, pain, and consciousness demonstrated how to conduct rigorous empirical research to understand non-human mental capacities and experience. Victoria formed our working group and was a wellspring of information and inspiration, even as she faced illness and death. We would also like to thank Brad Wyble for his invaluable comments and consultation regarding attentional systems. Cassie Beck provided input into early discussions on this topic. We are also grateful to the editor and three anonymous reviewers for identifying areas in need of clarification.

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All authors developed the theoretical argument in joint discussion. Paula Droege was the principal author of the text; Daniel Weiss provided substantial additions, revisions, and suggestions; Natalie Schwob and Victoria Braithwaite also contributed revisions and suggestions.

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Correspondence to Paula Droege.

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Victoria Braithwaite—Deceased.

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Droege, P., Weiss, D.J., Schwob, N. et al. Trace conditioning as a test for animal consciousness: a new approach. Anim Cogn (2021).

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  • Trace conditioning
  • Animal consciousness
  • Flexibility
  • Attention
  • Temporal representation theory