Neuroimaging Correlates of HumanAuditory BehaviorHST 722Brain Mechanisms for Hearing and SpeechOctober 27, 2005Jennifer Melcher"The Problem"SoundPerceptionNoninvasivePhysiologicMeasuresNeuralActivityFigure above illustrates how auditory evoked potentials are measured. Potential shown wasevoked by a click stimulus and was recorded in a human subject. Waveform is the averagedresponse to many click presentations. (AEP record from R.A. Levine)Furst et al. (1985) “Click lateralization is related to the βcomponent of the dichotic brainstem auditory evokedpotentials of human subjects”For binaural clicks with different ITDs and ILDs, quantifiedperceptionbinaural difference potential Attributes of the binaural difference are correlated withthe perception of binaural sound.Binaural difference (BD) is derived from BAEPs evoked bymonaural and binaural stimuli (above). BAEP: brainstem auditoryevoked potential The BD reflects an interaction between converging signalsfrom the two ears at the level of the brainstem.Binaural Difference PotentialFig. 9. Binaural, sum of the monaurals, and binaural difference waveforms for both species.The binaural (solid lines) and sum of the monaural waveforms (dotted lines) aresuperimposed. The difference between these two waveforms, the binaural difference (BD)waveform, is plotted below. The recording electrodes were vertex to nape for both species.Stimuli were 10/sec; rarefaction clicks at 40 dB SL for the cat and 38 dB HL for the human.(from Fullerton et al., 1987)Cellular Generators of the Binaural Difference PotentialCellular generators of the binaural difference potential in cat. Diagonal line shadingsindicate the generators of the first peak (‘b’; white on black) and possible generatorsof the second peak (‘d’; black on white). The schematic of the lower auditory system(at bottom) shows the generators’ relationship to other cells. NLL, nuclei of thelateral lemniscus; IC, inferior colliculus.(From Melcher, 1996)Discussion Questions:If the generator results are combined with the findings ofFurst et al., what can be said about the neural processingunderlying sound lateralization and binaural fusion?We generally think of the MSO as a coincidence detector.Are Furst et al.’s binaural difference data consistent with this idea?Late Responses: dependence on attention and stimulus contextIdealized AEP evoked by transient stimuli( ___ ) including components that are dependent onstimulus context and subject attention ( ….. , ----- ).(from Hillyard and Kutas, 1983; also see Hillyard etal., 1973; Donchin et al., 1978).ODDBALL PROCEDURETwo stimuli, S1 and S2Train with fixed intervalsProbabilities of S1 and S2 unequalS1 and S2 mixed randomlyFigure 1-12. Schematic diagram of oddballstimulus presentation paradigm for P300measurement (from Squires & Hecox, 1983).Selected measurement parameters areindicated. Responses are averaged separatelyfor Stimulus Type 1 (i.e. the frequent stimulus)and Stimulus Type 2 (i.e. the rare or oddballstimulus). Note. From “ElectrophysiologicalEvaluation of Higher Level AuditoryProcessing” by K.C. Squires and K.E. Hecox,1983, Seminars in Hearing, 4 (4), p. 422.Reprinted by permission.(from Hall, 1992)NdN2P3- or “processing negativity”- produced when the subject attends to the stimuli- visualized by taking the difference between responses to attended and unattended stimuli- or “N2000”, “mismatch negativity- occurs in response to “rare” stimuli (S2 below) in oddball paradigm- can occur even when the subject is not attending to the stimuli- dependent on stimulus modality (e.g. auditory vs. visual)- or “P300”- occurs in response to “rare” stimuli (S2 below) in oddball paradigm when the subject is attending to the stimuli- independent of stimulus modalityN2 (N200), P3 (P300)Fig. 1. Mean for eight subjects of the non-signal (NS), signal (S) and difference (Δ) waveforms at each electrode site in theauditory condition. Isopotential topographic distributions are expressed as percentages of maximum response amplitude forthe N1 and P2 components of the non-signal response (left) and the negative (N2 Δ) and positive (P3 Δ) components of theΔ waveform (right). Supraorbital (0) and vertex (electrode 3) traces from the 3 runs are superimposed.(From Simson et al., 1977)NS - responses to standard stimuli (2000 Hz tone bursts)S - responses to rare stimuli (1000 Hz tone bursts)Δ - response to rare stimuli minus response to standard stimuliFig. 4. Frontal, vertex, and parietal(across-subjects averaged) differencewaveforms obtained by subtracting theERP to the 1000-Hz standard stimulusfrom that to the 1044-Hz deviant stimulusat different deviant-stimulus probabilities.The continuous line indicates the countingcondition and the broken line the ignorecondition. The amplitude of the fronto-centrally distributed MMN is decreasedwhen the probability is increased from 2%to 10%. When the two stimuli areequiprobable, no MMN is seen.From Sams et al., 1985)MMN - mismatch negativityKraus et al. (1996) “Auditory neurophysiologic responsesand discrimination deficits in children with learning problems” Stimuli: Syllables, varied along two continua Subjects: Children with and without learning problems Measured discrimination and mismatch negativity The children with learning problems showed- deficits in their ability to discriminate syllables- abnormally small mismatch negativityConclusion The behavioral deficits in the children with learningproblems arose at a processing stage that precedes conscious perception.Brain ActivityIncreaseMetabolicResponseBlood FlowIncreaseTracerIncreaseBrain ActivityIncreaseMetabolicResponseBlood FlowIncreaseBloodOxygen-ationIncreaseImageSignalIncreasefMRI(Blood Oxygenation Level-Dependent (BOLD))PET(radioactive tracer e.g., radio-labeled H2O)Figure courtesy of I. Sigalovsky.Computational inflation of the corticalsurface. In the inflated format, the cortex ofsulci and gyri can be viewed simultaneously.See Fischl et al. (1999) NeuroImage 9: 195-207.Folded Cortex(lateral view)Inflated Cortex(lateral view)A B CTemporal Lobe(view from above)planum polareplanum temporaleHeschl’s gyruslateralanteriorSuperiorTemporal SulcusSylvianfissureHuman Brain(lateral view)Scott et al. (2000) “Identification of a pathway for intelligiblespeech in the left temporal lobe”Four stimulus conditions that included speech and severalforms of degraded