Some Observations on the Effects of Attention to Stimuli on the Amplitude of the Acoustically Evoked Response

Keating, Lawrence W.; Ruhm, Howard B.

doi:10.3109/00206097109072556

Cited by 20 publications

(2 citation statements)

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“…The results demonstrate that selective attention increases discrimination performance that depends on phase coherence but does not fundamentally alter the frequency-related discrimination profile. It seems reasonable to conjecture that task-related attention to a single stimulus, which is known to enhance the auditory evoked response over that observed for the passive listening condition (Keating and Ruhm, 1971), produces gain effects of the same nature. Thus, we would expect unattended stimuli to produce weaker phase coherence than attended stimuli, but not phase coherence increases in the absence of mean amplitude increases, in conflict with our current findings.…”

Section: Discussionmentioning

confidence: 99%

“…Subjects were instructed to decide if each stimulus was the modified or unmodified version of a sentence and to respond accordingly via a hand-held button press immediately after sentence completion. The sole purpose of this task was to keep subjects alert and attending to the stimuli in order to enhance the phase-locked evoked “signal” to background “noise” ratio (SNR) (Davis, 1964; Gross et al, 1965; Keating and Ruhm, 1971; Picton and Hillyard, 1974; Picton et al, 1971; Satterfield, 1965; Spong et al, 1965), as phase dissimilarity effects cannot be detected in single-trial data at low SNR levels. Subjects were allowed to rest between blocks and were instructed to change hands and then begin a new block (controlled by button press) when they were alert and ready.…”

Section: Methodsmentioning

confidence: 99%

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The neuromagnetic response to spoken sentences: Co-modulation of theta band amplitude and phase

Howard

Poeppel

2012

NeuroImage

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Speech elicits a phase-locked response in the auditory cortex that is dominated by theta (3–7 Hz) frequencies when observed via magnetoencephalography (MEG). This phase-locked response is potentially explained as new phase-locked activity superimposed on the ongoing theta oscillation or, alternatively, as phase-resetting of the ongoing oscillation. The conventional method used to distinguish between the two hypotheses is the comparison of post- to prestimulus amplitude for the phase-locked frequency across a set of trials. In theory, increased amplitude indicates the presence of additive activity, while unchanged amplitude points to phase-resetting. However, this interpretation may not be valid if the amplitude of ongoing background activity also changes following the stimulus. In this study, we employ a new approach that circumvents this problem. Specifically, we utilize a fine-grained time–frequency analysis of MEG channel data to examine the co-modulation of amplitude change and phase coherence in the post-stimulus theta-band response. If the phase-locked response is attributable solely to phase-resetting of the ongoing theta oscillation, then amplitude and phase coherence should be uncorrelated. In contrast, additive activity should produce a positive correlation. We find significant positive correlation not only during the onset response but also throughout the response period. In fact, transient increases in phase coherence are accompanied by transient increases in amplitude in accordance with a “signal plus background” model of the evoked response. The results support the hypothesis that the theta-band phase-locked response to attended speech observed using MEG is dominated by additive phase-locked activity.

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Section: Discussionmentioning

confidence: 99%