Blocking
The phenomenon of blocking provides an interesting and much-studied instance of failure to learn, in spite of contiguous presentations of CS and US. [blocking training an organism with one stimulus as a signal for an unconditioned stimulus to prevent the organism from learning about a second stimulus when both stimuli are subsequently presented together as signals for the same unconditioned stimulus] In a blocking experiment, animals receive training with what is termed a compound CS (Phase 2) – in this example represented by the simultaneous presentation of a noise and a light followed by a shock reinforcer. However, the experimental group has first received a phase of training in which the noise alone is conditioned (Phase 1). The performance of the control group of participants shows that training (Phase 2) with a compound CS is normally sufficient to establish associations between individual CS elements (noise, light) and the US (shock). So in this control group the light, when subsequently presented on ts own, will evoke a CR. But the experimental group shows no (or very little) evidence of learning about the light in Phase 2. Although they have received light–US pairings, just as the control participants have, in Phase 2, the formation of the light–US association appears to have been blocked by initial training with the noise in Phase 1. A possible explanation of the blocking effect links directly to the asymptote phenomenon. Recall that a US representation in a secondary state of activation will not support association formation. In our blocking experiment, Phase 1 training for the experimental group establishes the noise as a CS, enabling it to activate the US representation in a secondary state of activation. So for these participants, during Phase 2, the presentation of the US will not be able to produce the state of primary activation, which means that the light introduced as part of the CS at this stage of testing will be unable to acquire associative strength.
The phenomenon of blocking provides an interesting and much-studied instance of failure to learn, in spite of contiguous presentations of CS and US. [blocking training an organism with one stimulus as a signal for an unconditioned stimulus to prevent the organism from learning about a second stimulus when both stimuli are subsequently presented together as signals for the same unconditioned stimulus] In a blocking experiment, animals receive training with what is termed a compound CS (Phase 2) – in this example represented by the simultaneous presentation of a noise and a light followed by a shock reinforcer. However, the experimental group has first received a phase of training in which the noise alone is conditioned (Phase 1). The performance of the control group of participants shows that training (Phase 2) with a compound CS is normally sufficient to establish associations between individual CS elements (noise, light) and the US (shock). So in this control group the light, when subsequently presented on ts own, will evoke a CR. But the experimental group shows no (or very little) evidence of learning about the light in Phase 2. Although they have received light–US pairings, just as the control participants have, in Phase 2, the formation of the light–US association appears to have been blocked by initial training with the noise in Phase 1. A possible explanation of the blocking effect links directly to the asymptote phenomenon. Recall that a US representation in a secondary state of activation will not support association formation. In our blocking experiment, Phase 1 training for the experimental group establishes the noise as a CS, enabling it to activate the US representation in a secondary state of activation. So for these participants, during Phase 2, the presentation of the US will not be able to produce the state of primary activation, which means that the light introduced as part of the CS at this stage of testing will be unable to acquire associative strength.
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