Derrington, Krauskopf and Lennie (1984) characterised neural sensitivity in terms of the null-response of a neurone using the method of 'silent-substitution'. This means, in their terms that…

Question

BlackTom AI · Accepted Answer

Neuronal response can be modeled as a weighted sum of cone excitations: R = wL·ΔL + wM·ΔM + wS·ΔS. Silent substitution chooses a pattern of ΔL, ΔM, ΔS that produces nonzero changes in cone excitations but satisfies R = 0. In other words, it finds a stimulus direction in cone-contrast space that is orthogonal to the neurone’s weight vector (wL, wM, wS), producing no change in firing — a null-response.

Relevant knowledge points and concepts
- Cones (L, M, S) provide the photoreceptor inputs; cortical or LGN neurons combine these inputs with specific weights.
- Silent substitution is a stimulus-design technique that changes some cone excitations while keeping others effectively “silent” for the targeted neuron’s output by balancing contrasts.
- The null-response (zero change in firing) reveals the stimulus direction to which the neurone is insensitive; it defines the neurone’s null axis in color (cone-contrast) space.

Step-by-step reasoning
1. Represent the neurone’s linear response as R = wLΔL + wMΔM + wSΔS.
2. Silent substitution constructs ΔL, ΔM, ΔS such that at least one cone contrast is changed yet R = 0. That requires solving wLΔL + wMΔM + wSΔS = 0 for nontrivial Δ values.
3. Any nonzero solution defines a stimulus direction that leaves the neurone’s firing unchanged: the neuron is insensitive to that particular combination of cone contrasts.
4. By finding such null directions systematically, Derrington, Krauskopf and Lennie characterized the neurone’s sensitivity profile (which directions produce responses and which do not).

Why the correct answer is correct
- The null-response by definition identifies the stimulus direction producing no change in the neuron’s activity — i.e., the stimulus the neurone is insensitive to. Silent substitution is explicitly used to reveal those insensitive directions in cone-contrast space.

Why the other options are incorrect
- “Most sensitive to”: would require finding the stimulus that maximizes R, not the null-response.
- “Most variable response”: variability is about response variance across trials, not the null direction.
- “Only slightly sensitive to”: “slightly sensitive” implies a small but nonzero response; null-response specifically denotes no response, so this is incorrect.

Conclusion
Silent substitution as used by Derrington, Krauskopf and Lennie identifies the stimulus the neurone was insensitive to. This matches the provided correct answer: they identified the stimulus the neurone was insensitive to.

Derrington, Krauskopf and Lennie (1984) characterised neural sensitivity in terms of the null-response of a neurone using the method of 'silent-substitution'. This means, in their terms that…单项选择题

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