Psychophysical and neurometric detection performance under stimulus uncertainty

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Abstract

Signal detection theoretical analyses of spike counts have revealed that some cortical neurons can exceed psychophysical sensitivity in cases where a sensory signal is specified exactly. It is not known whether this finding holds in the more natural situation where signal occurrence is temporally uncertain. We investigated the ability of rat barrel cortex neurons to detect faint and transient whisker deflections occurring at unspecified times. The progression from fully specified stimuli to temporal uncertainty degraded neuronal sensitivity such that it seems highly unlikely that single neurons can provide the basis for decoding uncertain perceptual events. However, modeling the sensitivity of neuronal pools on basis of spike timing precision across several neurons in an optimal encoding window of 25 ms showed that the subject's perceptual sensitivity could be based on the occurrence of coincident spikes from four to five neurons.

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Figure 1: Behavioral protocol and psychometric data.
Figure 2: Firing properties of barrel cortex neurons and comparison with slowly adapting trigeminal ganglion fibers.
Figure 3: Identification of optimal encoding windows.
Figure 4: Psychometric precision acts as upper bound for neurometric precision of barrel cortex neurons.
Figure 5: Barrel cortex single units fire low numbers of spikes in response to whisker deflections but may reach high sensitivities.
Figure 6: Monte Carlo procedure to estimate sensitivities of neuronal pools.
Figure 7: Comparison of simulated sensitivity of neuronal pools with that measured from the rat observers.

Change history

  • 13 August 2008

    In the version of this article initially published online, the second sentence of the Figure 6 legend contained an incorrect number. The number should be 500 rather than 5,000. The error has been corrected in the print, PDF and HTML versions of this article.

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Acknowledgements

This work was funded by the Deutsche Forschungsgemeinschaft (SFB550 B11). M.C.S. was supported by a scholarship from the Studienstiftung des deutschen Volkes. We thank F. Jäkel and M. Bethge for helpful discussions concerning signal detection theory and design of the probabilistic model and U. Pascht for excellent technical assistance.

Author information

M.C.S. and C.S. designed the experiments; M.C.S. performed the experiments; M.C.S. and C.S. conducted data analyses and wrote the paper.

Correspondence to Cornelius Schwarz.

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Stüttgen, M., Schwarz, C. Psychophysical and neurometric detection performance under stimulus uncertainty. Nat Neurosci 11, 1091–1099 (2008) doi:10.1038/nn.2162

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