Forward Masking Estimated by Signal Detection Theory Analysis of Neuronal Responses in Primary Auditory Cortex

Abstract

Psychophysical forward masking is an increase in threshold of detection of a sound (probe) when it is preceded by another sound (masker). This is reminiscent of the reduction in neuronal responses to a sound following prior stimulation. Studies in the auditory nerve and cochlear nucleus using signal detection theory techniques to derive neuronal thresholds showed that in centrally projecting neurons, increases in masked thresholds were significantly smaller than the changes measured psychophysically. Larger threshold shifts have been reported in the inferior colliculus of awake marmoset. The present study investigated the magnitude of forward masking in primary auditory cortical neurons of anaesthetised guinea-pigs. Responses of cortical neurons to unmasked and forward masked tones were measured and probe detection thresholds estimated using signal detection theory methods. Threshold shifts were larger than in the auditory nerve, cochlear nucleus and inferior colliculus. The larger threshold shifts suggest that central, and probably cortical, processes contribute to forward masking. However, although methodological differences make comparisons difficult, the threshold shifts in cortical neurons were, in contrast to subcortical nuclei, actually larger than those observed psychophysically. Masking was largely attributable to a reduction in the responses to the probe, rather than either a persistence of the masker responses or an increase in the variability of probe responses.

Ability of primary auditory cortical neurons to detect amplitude modulation with rate and temporal codes: neurometric analysis

“…In the case of SC, across-cell correlation has been noted to reduce the effectiveness of pooling (Alves-Pinto et al 2010;Zohary et al 1994; for a counterexample, see Romo et al 2003). Since our pooling methods (except in the case of the multiunit considered as a pool) combine trials that were collected at different times, any correlation in SC that might have been present in an in vivo pooling operation will be missing in our simulation, and our SC threshold estimates may be too low (i.e., too sensitive) to the extent that we have failed to capture existing correlations.…”

Spatial and temporal disparity in signals and maskers affects signal detection in non-human primates

“…However, the large variability in forward masking in their dataset makes difficult to reconcile their neuronal threshold shifts with psychophysical threshold shifts. Alves-Pinto et al (2010) explored the magnitude of forward masking by recording from neurons on the auditory cortex of anesthetized guinea pigs. They found that threshold shifts were larger in the cortex compared to those observed in subcortical areas, suggesting that cortical processes might be involved in forward masking.…”

Comodulation Enhances Signal Detection via Priming of Auditory Cortical Circuits

“…This latter observation suggests that slow adaptation to temporal coherence across-frequency is necessary to implement this form of CMR. The nature of such adaptation is not known but could include cortical synaptic depression (Carandini et al, 2002; Chung et al, 2002; Freeman et al, 2002), forward suppression (Wehr and Zador, 2005; Alves-Pinto et al, 2010; Scholes et al, 2011), and/or modulation at subcortical processing stations via cortical feedback (Bajo et al, 2007; Malmierca and Ryugo, 2011). …”