Mismatch Paradigm Research Articles

Location changes enhance hemispheric asymmetry of magnetic fields evoked by lateralized sounds in humans

Auditory mismatch negativity, the brain's change-detection response, has been shown to be more sensitive than other early auditory cortex responses to the hemispheric specialization of speech processing. The present study used magnetoencephalography to assess hemispheric differences in cortical evoked responses during auditory spatial processing. We compared N1m to lateralized vowels presented with equal probabilities with mismatch fields (MMNm) to rare lateralized noises interspersed in a sequence of frequent midline sounds. Both N1m and MMNm dipole amplitudes were higher in the hemisphere contralaterally to the side of sound lateralization, but this effect was about four times bigger in the mismatch paradigm. Moreover, only MMNm dipoles showed shorter latencies in the hemisphere contralaterally to stimulation. Apparently stimulus changes activate specialized auditory networks more strongly than non-deviant events.

Acute Adaptation of the Vestibuloocular Reflex: Signal Processing by Floccular and Ventral Parafloccular Purkinje Cells

The gain of the vertical vestibuloocular reflex (VVOR), defined as eye velocity/head velocity was adapted in squirrel monkeys by employing visual-vestibular mismatch stimuli. VVOR gain, measured in the dark, could be trained to values between 0.4 and 1.5. Single-unit activity of vertical zone Purkinje cells was recorded from the flocculus and ventral paraflocculus in alert squirrel monkeys before and during the gain change training. Our goal was to evaluate the site(s) of learning of the gain change. To aid in the evaluation, a model of the vertical optokinetic reflex (VOKR) and VVOR was constructed consisting of floccular and nonfloccular systems divided into subsystems based on the known anatomy and input and output parameters. Three kinds of input to floccular Purkinje cells via mossy fibers were explicitly described, namely vestibular, visual (retinal slip), and efference copy of eye movement. The characteristics of each subsystem (gain and phase) were identified at different VOR gains by reconstructing single-unit activity of Purkinje cells during VOKR and VVOR with multiple linear regression models consisting of sensory input and motor output signals. Model adequacy was checked by evaluating the residual following the regressions and by predicting Purkinje cells' activity during visual-vestibular mismatch paradigms. As a result, parallel changes in identified characteristics with VVOR adaptation were found in the prefloccular/floccular subsystem that conveys vestibular signals and in the nonfloccular subsystem that conveys vestibular signals, while no change was found in other subsystems, namely prefloccular/floccular subsystems conveying efference copy or visual signals, nonfloccular subsystem conveying visual signals, and postfloccular subsystem transforming Purkinje cell activity to eye movements. The result suggests multiple sites for VVOR motor learning including both flocculus and nonflocculus pathways. The gain change in the nonfloccular vestibular subsystem was in the correct direction to cause VOR gain adaptation while the change in the prefloccular/floccular vestibular subsystem was incorrect (anti-compensatory). This apparent incorrect directional change might serve to prevent instability of the VOR caused by positive feedback via the efference copy pathway.

Right-Hemisphere Dominance for the Processing of Sound-Source Lateralization

Cortical processing of change in direction of a perceived sound source was investigated in 12 human subjects using whole-head magnetoencephalography. The German word "da" was presented either with or without 0.7 msec interaural time delays to create the impression of right- or left-lateralized or midline sources, respectively. Midline stimuli served as standards, and lateralized stimuli served as deviants in a mismatch paradigm. Two symmetrically linked dipoles fitted to the mismatch fields showed stronger moments in the hemisphere contralateral to the side of the deviant. The right dipole displayed equal latencies to both left and right deviants, whereas left dipole latencies were longer for ipsilateral than contralateral deviants. Frequency analysis between 20-70 Hz and statistical probability mapping revealed increased induced gamma-band activity at 53+/-2.5 Hz to both types of deviants. Right deviants elicited spectral amplitude enhancements in this frequency range, peaking at latencies of 160 and 240 msec. These effects were localized bilaterally over the angular gyri and posterior temporal regions. Coherence analysis suggested the existence of two separate interhemispheric networks. For left-lateralized deviants, both spectral amplitude enhancements at 110 and 220 msec and coherence increases were restricted to the right hemisphere. In conclusion, both mismatch dipole latencies at the supratemporal plane and gamma-band activity in posterior parietotemporal areas suggested a right hemisphere engagement in the processing of bidirectional sound-source shifts. In contrast, left-hemisphere regions responded predominantly to contralateral events. These findings may help to elucidate phenomena such as unilateral auditory neglect.

Match-mismatch of fear, panic and performance

The present study tested predictions derived from Rachman's match-mismatch theory of fear. Students ( N = 117) displaying claustrophobic fear made predictions of fear, panic and performance prior to exposure to a claustrophobic chamber. Subjects were then classified into groups (i.e. matchers, overpredictors, underpredictors) based on the congruence between their anticipated phobic reactions and their actual reactions during exposure. The effects of match-mismatch status on predictions of fear, panic and performance on a subsequent exposure trial were examined. Results provided further evidence that phobic Ss are frequently inaccurate in predicting their phobic reactions during exposure. Consistent with previous findings, Ss who overpredicted fear, panic or performance tended to lower their predictions on a subsequent exposure trial, whereas Ss who underpredicted fear, panic or performance showed heightened predictions upon subsequent exposure. Contrary to previous findings, Ss were more likely to underpredict rather than overpredict their phobic reactions. Our findings are in accord with those of Rachman indicating that the magnitude of mismatch between predicted and actual fear/panic is more influential in determining subsequent predictions of fear/panic than it is in determining Ss' actual fear/panic. Moreover, this asymmetry was observed when the mismatch paradigm was applied to phobic behavior (i.e. tendency to escape).

Plurality of Viual Mismatch Potentials in a Reptile

Abstract Studies with auditory stimuli have established in humans that a mismatch potential (MMP) is elicited whenever a deviant stimulus is substituted for a standard stimulus in a train of monotonous standard stimuli presented at rates > 0.25 Hz. The MMP in humans is localized in the auditory cortex and is known as mismatch negativily, from its polarity in scalp recordings. It is hypothesized to reflect the operation of sensory memory and to be a necessary component of the auditory orienting response. To examine the generality of MMPs we used a visual mismatch paradigm with pond turtles (Pseudemys scripta) while recording with electrode arrays (200 μm spacing) from near surface and deep visual projection areas within the forebrain and optic tectum. Standard stimuli were 10-sec trains of diffused strobe flashes presented at rates of 1-6 Hz against backgrounds of 2-11 lux. Deviant stimuli were brighter or dimmer flashes that followed the last standard flash. MMps were separated from visual evoked potentials by subtracting the response to the last standard flash of the train from the response to the same flash (bright or dim) when delivered as a deviant. Comparisons were also made with evoked potentials to isolated bright or dim flashes, that is, equal in frequency (1 per 12 sec) to the deviants but without intervening standard flashes. At tectal loci bright and dim deviants elicited net positivities that reached statistical significance in the period between 141 ± 8 and 184 ± 12 msec after the deviant stimulus (mean ± SEM). Earlier components in the tectal responses correlated with the intensity of the stimulus rather than its deviance. In the case of the bright deviants the early waves (P50-P75) were larger in amplitude. Forebrain recordings showed a similar although broader period of net positivity, associated with deviance, between 129 ± 8 and 195 ± 12 msec. Deviants, delivered as isolated flash responses evoked larger early components (100-140 msec). In separate experiments with cortical epipial electrodes, a condition somewhat more comparable to scalp recording, MMPs were similar in latency but had a negative polarity. Regression analyses revealed a relationship between the amplitude (base-to-peak) of the MMF' and the degree to which the standard response had declined with repeated stimulation. Rate decrement, as measured by the isolated (long ISI) flash response minus the last standard response, was a significant predictor of MMP amplitudes (r(2) = 0.37, tectum; r(2) = 0.31, forebrain), whereas standard response amplitudes alone were not (r(2) = 0.09; r(2) = 0.06). MMPs are present in nonmammals plurally, that is, at different levels of the visual system, at least as early as the tectum. The existence of subcortical MMPs caution against assigning a primary or exclusive role to those recorded from the cortex.