Article Figures & Data
Figures
- Figure 1.
Summary of data analysis methods and a sample neuron showing the complex nature of multisensory enhancement: multisensory stimuli shorten response latencies and enhance response magnitude. A, Illustration of how the impulse raster is converted into the qsum, the bounding window (B, E) identified, and the response onset (R) determined. B, Comparison of the performance of the algorithm against common algorithms based on spike density functions (SDF) and instantaneous firing rate (IFR) when the spontaneous rate is 5 Hz. Plotted is the median error (actual first impulse time minus algorithm decision) of >500 simulations of 30 trials in which a 100 ms response (stimulus-driven rate on x-axis) with a 100 ms response onset delay was embedded in a 1 s trial. See text for more details. C, The statistical criterion for detecting significant responses (critical p value) is adjusted to ensure a 95% confidence level. Different spontaneous rates require different critical p values (circles, read off of the log-scaled left axis), a relationship described by a piecewise continuous exponential-log function (solid line). If the critical p value is not corrected from 0.05, the percentage of false positives can be <5 or >5%, depending on the spontaneous rate (x's, read off of the linearly scaled right axis). D, Top, Impulse rasters (dots) from a sample neuron. Bottom, The window of interest (50–150 ms) is expanded (black dots, multisensory impulses; gray dots, auditory; visual impulses are not visible in this window). Shown are the response onsets (vertical lines) and multisensory and unisensory qsums (solid lines, use right axis). Note that the onset of the multisensory response began 19 ms before the onset of the earliest unisensory (i.e., auditory) response. Also, note that at the time of the very first auditory response, the multisensory response is already enhanced. V, Visual; A, auditory; VA, multisensory.
- Figure 2.
Multisensory stimuli evoke speeded responses. A, The probability distributions (gray bars, left axis) and cumulative distribution functions (solid curves plotted below, right axis) for response latency shifts produced by multisensory integration (multisensory latency, shortest unisensory latency). Cross-modal stimulus conditions are divided into two categories: those in which both modality-specific stimulus components produce responses individually (i.e., when alone), and those in which only the auditory stimulus is effective. B, The percentage of stimulus conditions that produced speeded responses in each of the bimodal neurons studied.
- Figure 3.
The temporal profile of multisensory enhancement. Shown are the mean differences between the multisensory and best unisensory qsums (Î ı qsum, refer to the left axis) and the mean proportionate enhancement (MSI, refer to the right axis) at each moment in time. All data are time-shifted so that the earliest unisensory response began at 0 ms for the two categories described in the text. MSI was greatest before the onset of the referent unisensory response, because the unisensory referent was zero. MSI decreased within 40 ms to approximately stable values of 120% (top) and 35% (bottom). Inserts show the distributions (across conditions) of Î ı qsums at selected moments in time (50 and 1 ms before the earliest unisensory response).
- Figure 4.
Computational impact of latency shifts. A, The mean difference between the multisensory and summed unisensory responses for conditions in which both modality-specific stimuli occur before any response (0 = earliest response onset). The multisensory computation was initially superadditive (box, vertical arrow), then transitioned to additive within 40 ms. Inserts show the distributions (across conditions) of Î ı qsums at selected moments in time (50 and 1 ms before the earliest unisensory response). B, The percentage of conditions producing superadditive computations at or before each moment in time (0 = earliest unisensory response). Eighty-eight percent of conditions producing enhancement contained a superadditive computation 69% of the time before the earliest unisensory response.
