Sensitivity of neurons in cat primary auditory cortex to tones and frequency-modulated stimuli. I: Effects of variation of stimulus parameters
ABSTRACT In the primary auditory cortex (AI) of barbiturate-anesthetized cats multi-unit responses to tones and to frequency-modulated (FM) tonal stimuli were analyzed. Characteristic frequency (CF), sharpness of tuning, minimum threshold, and dynamic range of spike count--intensity functions were determined. Minimum threshold and dynamic range were positively correlated. The response functions to unidirectional FM sweeps of varying linear rate of change of frequency (RCF) that traversed the excitatory frequency response areas (FRAs) displayed a variety of shapes. Preferences for fast RCFs (> 1000 kHz/s) were most common. Best RCF was not correlated with measures of sharpness of tuning. Directional preference and sensitivity were quantified by a DS index which varied with RCF. About two-thirds of the multi-unit responses showed a preference for downward sweeps. Directional sensitivity was independent of CF and independent of best RCF. Measurements of latencies of phasic responses to unidirectional FM sweeps of different RCF demonstrated that the discharges of a given multi-unit over its effective RCF range were initiated at the same instantaneous frequency (effective Fi), independent of RCF. Effective Fis fell within the excitatory FRA of a given multi-unit. The relationships of effective Fis to CF show that responses were evoked only when the frequency of the signal was modulated towards CF and not when modulated away from it, and that responses were initiated before the modulation reached CF. Changes in the range and depth of modulation had only minor, if any, effects on RCF response characteristics, FM directional sensitivity, and effective Fis, as long as the beginning and ending frequencies of FM sweeps fell outside a multi-unit's FRA. Stimulus intensity also had only moderate effects on RCF response characteristics and DS. However, effective Fis were influenced in systematic fashions; with increases in intensity, effective Fis to upward and downward sweeps decreased and increased, respectively. Thus, for higher intensities FM responses were initiated at instantaneous frequencies occurring earlier in the signal. The results are compared with previous data on tone and FM sensitivity of auditory neurons in cortical and subcortical structures, and mechanisms of FM rate and directional sensitivity are discussed. The topographic representations of these neuronal properties in AI are reported in the companion report.
- SourceAvailable from: Gavin Bidelman
[Show abstract] [Hide abstract]
- "In contrast, others have reported no perceptual asymmetries between rising and falling glides   . Still others have shown the opposite pattern where listeners achieve higher sensitivity for downward compared to upward sweeping pitch  . However, as noted by Luo, et al. , a behavioral up/down asymmetry in frequency modulation perception is likely clouded by subjective bias (and/or language experience) of the observer. "
ABSTRACT: Event-related brain potentials (ERPs) demonstrate that human auditory cortical responses are sensitive to changes in static pitch as indexed by the pitch onset response (POR), a negativity generated at the initiation of acoustic periodicity. Yet, it is still unclear if this brain signature is sensitive to dynamic, time-varying properties of pitch more characteristic of those found in naturalistic speech and music. Neuroelectric PORs were recorded in response to contrastive pitch patterns differing in their pitch height, time-variance, and directionality (i.e., rise vs. fall). Broadband noise followed by contiguous iterated rippled noise (producing salient pitch sweeps) was used to temporally separate neural activity coding the onset of acoustic energy from the onset of time-varying pitch. Analysis of PORs revealed distinct modulations in response latency that distinguished static from time-varying pitch contours (steady-state < dynamic) and pitch height (high < low). However, PORs were insensitive to the direction of pitch sweeps (rise=fall). Our findings suggest that the POR signature provides a useful neural index of auditory cortical pitch processing for some, but not all pitch-evoking stimuli. Copyright © 2015. Published by Elsevier Ireland Ltd.Neuroscience Letters 07/2015; 603. DOI:10.1016/j.neulet.2015.07.018 · 2.03 Impact Factor
[Show abstract] [Hide abstract]
- "While most neurons respond to a broad range of modulation rates and to both upward and downward FM sweeps , , selectivity for the direction of FM sweeps could be found along the tonotopic gradient in the monkey auditory cortex. Low-frequency neurons appeared to prefer upward and high-frequency neurons downward FM sweeps , . "
ABSTRACT: Decoding of frequency-modulated (FM) sounds is essential for phoneme identification. This study investigates selectivity to FM direction in the human auditory system. Magnetoencephalography was recorded in 10 adults during a two-tone adaptation paradigm with a 200-ms interstimulus-interval. Stimuli were pairs of either same or different frequency modulation direction. To control that FM repetition effects cannot be accounted for by their on- and offset properties, we additionally assessed responses to pairs of unmodulated tones with either same or different frequency composition. For the FM sweeps, N1m event-related magnetic field components were found at 103 and 130 ms after onset of the first (S1) and second stimulus (S2), respectively. This was followed by a sustained component starting at about 200 ms after S2. The sustained response was significantly stronger for stimulation with the same compared to different FM direction. This effect was not observed for the non-modulated control stimuli. Low-level processing of FM sounds was characterized by repetition enhancement to stimulus pairs with same versus different FM directions. This effect was FM-specific; it did not occur for unmodulated tones. The present findings may reflect specific interactions between frequency separation and temporal distance in the processing of consecutive FM sweeps.PLoS ONE 12/2010; 5(12):e15548. DOI:10.1371/journal.pone.0015548 · 3.23 Impact Factor
[Show abstract] [Hide abstract]
- "Previous electrophysiological studies generally evaluated the direction sensitivity of a neuron by comparing the mean firing rates of upward and downward sweeps. This method has revealed that many A1 neurons have a preference for upward or downward sweep     . Some studies also found that the direction preference is topographically ordered in parallel with BF or CF    , whereas others have not observed such a relationship   . "
ABSTRACT: Neural responses to frequency modulated (FM) sweeps have been well investigated in single-units using electrophysiological recording methods. However, rare psychophysical experiments were conducted to investigate behavioral discrimination of FM-sweeps in the same species used in physiological experiments. Also, the previous studies have not focused on how the population of cortical neurons works together to encode the direction of FM-sweeps. To investigate the relation between the behavioral perception of FM direction and the population coding, we examined the cat's capability to discriminate the upward and downward FM-sweeps and recorded the neural responses to the same stimuli from the primary auditory cortex (A1) in different awake cats. We found that cats showed high performance to detect the change of direction of FM-sweeps, which linearly swept between 0.1 and 16kHz in 40-160ms duration; however, the behavioral performance obviously deteriorated when the sweeps were shortened to 10-20ms. Physiological results indicated that the upward sweeps elicited a temporal sequence of responses among the A1 neurons, in which neurons tuning to low-frequencies responded earlier and those tuning to high-frequencies later, while the response sequence was reversed when A1 was driven by the downward sweeps. The rank-order of response latencies could provide a reliable discrimination of the FM direction, and the discrimination performance paralleled with the cat's behavioral performance. Our result suggests that the relative response timings in A1 contain enough information used by subsequent processing stages to make the decision of FM direction.Behavioural brain research 11/2010; 217(2):315-25. DOI:10.1016/j.bbr.2010.10.034 · 3.03 Impact Factor