A long-latency response component (N1m) and the sustained field (SF) of the auditory evoked magnetic field elicited by two composite stimuli (a two-tone combination and a two-formant vowel) and their individually presented components (a 600-Hz and a 2100-Hz pure tone and two single-vowel formants with formant frequencies matched to the tone frequencies) were recorded using a 37-channel magnetometer. The response to the composite stimuli differed from the linear sum of the responses to the respective components in latency, equivalent dipole moment, and equivalent dipole location, suggesting an interaction among the processes elicited by the constituents of composite stimuli. N1m and SF source locations were more medial for the response to the high tone than to the low tone and more medial for the response to the high vowel formant than to the low vowel formant. The N1m formant sources were more lateral than the N1m tone sources. These findings suggest that, at the level of the auditory cortex, vowels are represented in terms of both the spectral pitches determined by their most prominent harmonics and, within the latency range of the N1m, the virtual pitch determined by the spacing of the harmonics.

Using an electronic tight-binding theory we calculate the nonlinear magneto-optical response from an x-Cu/1Fe/Cu(001) film as a function of frequency and Cu overlayer thickness (x=3. . .25). We find very strong spinpolarized quantum well oscillations in the nonlinear magneto-optical Kerr effect (NOLIMOKE). These are enhanced by the large density of Fe d states close to the Fermi level acting as intermediate states for frequency doubling.In good agreement with experiment we find two oscillation periods of 6-7 and 11 monolayers the latter being more pronounced. Typeset using REVT E X 1The magnetism of low-dimensional metallic structures such as surfaces, thin films, and multilayer sandwiches has recently become an exciting new field of research and applications [1]. In particular, thin magnetic films and multilayers exhibit a rich variety of properties not previously found in bulk magnetism such as enhanced or reduced moments [2], oscillatory exchange coupling through nonmagnetic spacers [3][4][5], giant magnetoresistance [6,7], and the reorientation of the magnetic easy axis upon thickness and temperature variation [8][9][10][11]. Especially the observation of spin-polarized quantum well states (QWS) [12][13][14][15] in Cu/Co (001) has attracted a great deal of attention. It has become clear that quantum well states are indeed responsible for the important oscillatory behavior of the exchange coupling of ferromagnetic thin films via nonmagnetic spacers [16,17]. Presently mainly photoemission (PE) and inverse photoemission (IPE) [12][13][14][15] have been used to identify QWS effects. Very recently a possible connection between thickness dependent changes in NOLIMOKE and QWS [18] has been proposed.It is the goal of this Letter to show that also nonlinear optics, in particular NOLIMOKE, is a new sensitive tool for studying QWS. We find very interesting structure in the NO-LIMOKE signal due to particular transitions in k-space. This is very remarkable since it indicates that NOLIMOKE is able to detect very sensitively k-dependent structures. This new effect seems to be of general interest for the physics of nonlinear optics and its relationship to the underlying electronic structure. Note, this is not the case for linear optics, since there the contribution of the Drude term of the dielectric function creates a strong background of transitions from all k-directions. Nonlinear optics, in contrast to linear op-

Auditory-evoked mismatch fields (MMFs) elicited by vowel contrasts and plosive stop consonant place-of-articulation contrasts were recorded over the left hemisphere of neurologically and audiologically normal subjects. Two experiments were conducted: vowels were presented in isolation in experiment 1 and embedded in consonant-vowel syllables in experiment 2. Bestfit equivalent MMF sources were obtained using the model of a single, spatiotemporal current dipole in a sphere. In both experiments, MMF sources activated by place-of-articulation contrasts were later in latency and smaller in dipole moment amplitude than MMF sources excited by vowel contrasts. There was evidence, albeit not unambiguous, for the vowel-contrast MMF sources being located more posteriorly than the consonant-contrast MMF sources in experiment 1 and more laterally in experiment 2. In both experiments, the MMF source excited by the contrast between /da/ and /ga/ was more anterior than the MMF source excited by the contrast between /da/ and /ba/. The effects on latency and dipole moment may be interpreted to mirror differences in perceptual discriminability and auditory memory decay between consonantal place-of-articulation contrasts and vowel contrasts. Similarly, the effects on location may be interpreted to reflect featural specificity of the mismatch response. Interestingly, the dipole source analysis results show a correspondence to the pattern of preservation and loss of the mismatch response to vowel and consonant place-of-articulation contrasts recently observed in Wernicke's aphasia.

We analyze second-harmonic generation ͑SHG͒ oscillations due to quantum-well states in ultrathin overlayer films and their dependence on the electronic and magnetic structure of the film and substrate. Depending on the SHG contribution from the surface and the film-substrate interface, and the interplay between the wave-function symmetry ͑via the dipole matrix elements͒ and band-structure effects, one obtains different SHG oscillations as a function of film thickness. One may obtain only one period, which is twice that observed in the linear magneto-optical Kerr effect ⌳ M , but also ⌳ M and an additional, larger period. Thus we explain, within a unified approach, recent experiments on x-Au/Co͑0001͒/Au͑111͒ and x-Cu/Fe/Cu͑001͒ films, where different characteristic features of the SHG oscillations and different oscillation periods were observed.

The auditory-evoked neuromagnetic field elicited by single vowel formants and two-formant vowels was recorded under active listening conditions using a 37-channel magnetometer. There were three single formants with formant frequencies of 200, 400, and 800 Hz, another single formant with a formant frequency of 2600 Hz, and three vowels that were constructed by linear superimposition of the high- onto one of the low-frequency formants. P50 m and N100 m latency values were inversely correlated with the formant frequency of single formants. A strong effect of formant frequency on source location was obtained along the postero-anterior axis, which is orthogonal to the well-established latero-medial tonotopic gradient. Regardless of whether single formants or first formants of vowels were considered, N100 m sources were more anterior and sustained field sources were more posterior for higher-frequency than for lower-frequency formants. The velocity of the apparent posterior-to-anterior movement across cortical surface of N100 m sources first reported by Rogers et al. [Rogers, R. L., Papanicolaou, A. C., Baumann, S. B., Saydjari, C., & Eisenberg, H. M. (1990). Neuromagnetic evidence of a dynamic excitation pattern generating the N100 auditory response. Electroencephalography and Clinical Neurophysiology,77, 237-240] decreased as a function of latency. The amount of deceleration was positively correlated with formant frequency. Responses to the vowels were superadditive, indicating that the processes elicited by the constituents of composite stimuli interact at one or more stages of the afferent auditory pathway. Such interaction may account for the absence of a lateral-to-medial tonotopic mapping of first formant frequency. The source topography found may reflect activity in auditory fields adjacent to AI with the strength of the contribution varying with formant frequency. Alternatively, it may reflect sharpness-of-tuning and inhibitory response-area asymmetry gradients along isofrequency stripes within AI. Either alternative may be interpreted in terms of a spectral blurring mechanism that abstracts spectral envelope information from the details of spectral composition, an important step towards the formation of invariant phonetic percepts.