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Link to original content: https://pubmed.ncbi.nlm.nih.gov/20826671/
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. 2010 Sep 8;30(36):12084-93.
doi: 10.1523/JNEUROSCI.0827-10.2010.

Competing streams at the cocktail party: exploring the mechanisms of attention and temporal integration

Juanjuan Xiang  1 , Jonathan Simon, Mounya Elhilali
Affiliations

Competing streams at the cocktail party: exploring the mechanisms of attention and temporal integration

Juanjuan Xiang et al. J Neurosci. .

Abstract

Processing of complex acoustic scenes depends critically on the temporal integration of sensory information as sounds evolve naturally over time. It has been previously speculated that this process is guided by both innate mechanisms of temporal processing in the auditory system, as well as top-down mechanisms of attention and possibly other schema-based processes. In an effort to unravel the neural underpinnings of these processes and their role in scene analysis, we combine magnetoencephalography (MEG) with behavioral measures in humans in the context of polyrhythmic tone sequences. While maintaining unchanged sensory input, we manipulate subjects' attention to one of two competing rhythmic streams in the same sequence. The results reveal that the neural representation of the attended rhythm is significantly enhanced in both its steady-state power and spatial phase coherence relative to its unattended state, closely correlating with its perceptual detectability for each listener. Interestingly, the data reveal a differential efficiency of rhythmic rates of the order of few hertz during the streaming process, closely following known neural and behavioral measures of temporal modulation sensitivity in the auditory system. These findings establish a direct link between known temporal modulation tuning in the auditory system (particularly at the level of auditory cortex) and the temporal integration of perceptual features in a complex acoustic scene, while mediated by processes of attention.

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Figures

Figure 1.
Figure 1.
Stimulus design. The stimulus consists of two pure tone sequences, one at a low rhythm and one at a fast rhythm. The spectral distance between the two streams is fixed as ±8 semitones. In each task, listeners are instructed to track either the slow or fast stream while ignoring the other one and detect a temporal jitter in the target stream. H, High; L, low.
Figure 2.
Figure 2.
Behavioral and neural responses. a, Behavioral performance results for 4 and 7 Hz tasks, measured by d′. The black color depicts performance measures obtained in the psychoacoustic study, and the gray depicts measures obtained in the MEG study for the same stimulus paradigm. Error bars represent SE. b, Power spectral density for the aSSR for a single subject while tracking the 4 Hz stream (top row) and 7 Hz (bottom row), averaged over 20 channels. Insets, The MEG magnetic field distributions of the 4 and 7 Hz rhythm response components. Red and green contours represent the target magnetic field strength projected onto a line with constant phase. c, Change in mean neural response at 4 and 7 Hz during both tasks, averaged across 26 listeners. Each bar represents the normalized neural power at a specific frequency (4 or 7 Hz) during the slow task (attend to 4 Hz) or fast task (attend to 7 Hz). The bars are color coded to match the colored arrows in b. Error bars represent SE. Inset, Correlation between change in neural response and behavioral performance of individual subjects. The slope, converted to an angle, of the normalized neural signal versus behavioral performance per subject yields a mean slope of 46.1°. Bootstrap estimates show 95% confidence intervals (gray background) and confirm the positive correlations between neural and behavioral measures. *p = 0.05, **p = 0.01.
Figure 3.
Figure 3.
Power and phase enhancement during the attended task. Left, Normalized neural response difference between slow and fast tasks shows enhancement exclusively at target rates (4 Hz for the slow task, 7 Hz for the fast task). Error bars represent SE. The asterisks at 4 and 7 Hz shows that only these frequencies yield a statistically significant enhancement. Middle, Phase coherence difference between the slow and fast tasks showing enhancement exclusively at target rates. Error bars represent SE. The difference between number of channel pairs with robust increased coherence and channel pairs with decreased coherence is normalized over the total number of long-range channel pairs. Right, Channel pairs with robust coherence difference at target rates for single subject, overlaid on the contour map of normalized neural response at target rates. The channel pairs with increased (decreased, respectively) coherence at target rates is shown by red (blue, respectively) lines.
Figure 4.
Figure 4.
Neural responses to target rates across hemispheres. The 20 channels with the strongest normalized neural response at target rates are chosen from left and right hemisphere, respectively, to represent the overall neural activity of each hemisphere. Neural responses averaged across the 20 channels are subtracted across hemispheres for each task and for all subjects. Error bars represent SE. **p < 0.04.
Figure 5.
Figure 5.
Buildup over time of behavioral and neural responses of target streams. Normalized neural response to the 4 Hz stream, and behavioral performance, as a function of time during the slow task averaged across subjects. Error bars represent SE. Top insets, The MEG magnetic field distributions of the 4 Hz target response for a single subject at representative moments in time. Bottom inset, Correlation of behavioral and neural responses as a function of time. The ratio of the neural to behavioral response trends as a function of time, interpreted as a slope angle, is averaged across subjects, yielding a mean slope angle of 22° (yellow line). Bootstrap estimates and the 95% confidence intervals (gray background) confirm the positive correlation between the psychometric and neurometric buildup curves.
Figure 6.
Figure 6.
Behavioral performance at different target rates. a, Behavioral performance results (d′) in a two-stream stimulus, as a function of target rate. Each pair of points with a similar color code indicates one psychoacoustic condition testing two specific rhythms. Error bars represent SE. b, Analysis of behavioral performance differentiating target, nontarget, and null (no deviant) trials for each of the three psychoacoustic conditions. The color code is similar to the one used in a. c, Normalized neural responses to the target rhythm (slow or fast) as a function of time during three psychoacoustic conditions and one MEG condition. Error bars represent SE. *p < 0.06, **p < 0.03.
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