Rapid Brain Discrimination of Rapid Brain Discrimination of Sounds of ObjectsSounds of Objects

Micah M. Murray,1,2 Micah M. Murray,1,2  Christian Camen,3  Christian Camen,3  Sara L. Gonzalez Andino,4 Pierre Bovet,3 and Sara L. Gonzalez Andino,4 Pierre Bovet,3 and Stephanie Clarke1 Stephanie Clarke1

1Neuropsychology Division and 2Radiology Service, The Functional Electrical Neuroimaging Laboratory, 1Neuropsychology Division and 2Radiology Service, The Functional Electrical Neuroimaging Laboratory, Hôpital Nestlé, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland, 3Faculté de Hôpital Nestlé, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland, 3Faculté de

Psychologie et des Sciences de l’Éducation, Geneva University, 1211 Geneva, Switzerland, and 4The Psychologie et des Sciences de l’Éducation, Geneva University, 1211 Geneva, Switzerland, and 4The Functional Brain Mapping Laboratory, Neurology Department, Geneva University Hospital, 1211 Geneva, Functional Brain Mapping Laboratory, Neurology Department, Geneva University Hospital, 1211 Geneva,

SwitzerlandSwitzerland

The Journal of Neuroscience, January 25, 2006The Journal of Neuroscience, January 25, 2006

IntroductionIntroduction How fast can the brain discriminate sounds? How fast can the brain discriminate sounds?

Related studies indicate that recognition and categorization of Related studies indicate that recognition and categorization of faces and objects can be achieved within ~150ms after stimulus faces and objects can be achieved within ~150ms after stimulus onset. onset.

Superior temporal sulcus shown to be involved in speech/ voice Superior temporal sulcus shown to be involved in speech/ voice recognition.recognition.

May be motor related or so called mirror neuron system.May be motor related or so called mirror neuron system.

Temporal information thought to play role in language acquisition Temporal information thought to play role in language acquisition and proficiency.and proficiency.

Evidence that specialization within auditory network might Evidence that specialization within auditory network might differentiate sound categories into tools vs. animals. differentiate sound categories into tools vs. animals.

The studyThe study

Used electrical neuroimaging (EEG)Used electrical neuroimaging (EEG)

Examined speed and the Examined speed and the neurophysiological mechanism by neurophysiological mechanism by which sounds of living and man-which sounds of living and man-made objects are first differentiated. made objects are first differentiated.

MaterialsMaterials 9 healthy subjects – 21-34 years of age9 healthy subjects – 21-34 years of age

• 6 females6 females• 3 males3 males• All right handedAll right handed• No history of illnessNo history of illness

• Used complex meaningful sounds from an on-Used complex meaningful sounds from an on-line libraryline library

• 16 bit stereo; 22,500Hz digitization16 bit stereo; 22,500Hz digitization• Used a set of 120 sounds as a database for Used a set of 120 sounds as a database for

selecting the sounds used for the EEG portion selecting the sounds used for the EEG portion of the study. of the study.

MethodsMethods In a pretest session, a separate group of 18 subjects listened to, identified, In a pretest session, a separate group of 18 subjects listened to, identified,

and gave a familiarity rating of the sound using a 1-7 Likert scale. and gave a familiarity rating of the sound using a 1-7 Likert scale.

The sounds that were most often correctly identified were used:The sounds that were most often correctly identified were used:

• 20 living/ 20 man-made20 living/ 20 man-made

Used audio editing to account for discrepancies between the sounds Used audio editing to account for discrepancies between the sounds including:including:• Each sound made to 500ms in lengthEach sound made to 500ms in length

• 50ms decay time applied to end of sound file to minimize clicks @ offset50ms decay time applied to end of sound file to minimize clicks @ offset • Compared for acoustic differences and time frequenciesCompared for acoustic differences and time frequencies

• Harmonics-to-noise ratio( no significant differences)Harmonics-to-noise ratio( no significant differences)

Results showed that only significant differences were shown after ~125ms Results showed that only significant differences were shown after ~125ms of sound and for frequencies above ~4000Hz because an additional 15-of sound and for frequencies above ~4000Hz because an additional 15-20ms is required for signal transmission into the human auditory cortex. 20ms is required for signal transmission into the human auditory cortex.

Stimulus listStimulus list

Methods (Cont.)Methods (Cont.)

As an additional control a second group of As an additional control a second group of subjects were selected:subjects were selected:• 10 healthy subjects10 healthy subjects

5 male, 5 female5 male, 5 female 20-32 years of age20-32 years of age 8 right handed, 3 left8 right handed, 3 left

Listened to final set of 120 sounds.Listened to final set of 120 sounds.

Identified living vs. man-made and using Identified living vs. man-made and using 1-7 Likert scale rated their confidence, and 1-7 Likert scale rated their confidence, and familiarity with the sound. familiarity with the sound.

Procedure and taskProcedure and task Living vs. non-living oddball paradigm.Living vs. non-living oddball paradigm.

Target stimuli to which subjects pressed a response button Target stimuli to which subjects pressed a response button occurred 10% of the time, 90% were distracters.occurred 10% of the time, 90% were distracters.

300 trials with intervals of 3.4s.300 trials with intervals of 3.4s.

Each subject completed 4 blocks of trials (2man-made, 2 living).Each subject completed 4 blocks of trials (2man-made, 2 living).

Peristimulus epochs of continuous EEG averaged from each Peristimulus epochs of continuous EEG averaged from each subject separatly for each condition to compute auditory evoked subject separatly for each condition to compute auditory evoked potentials (AEPs).potentials (AEPs).

Baseline defined as 100ms prestimulus period.Baseline defined as 100ms prestimulus period.

Trials with blinks or eye movements were rejected.Trials with blinks or eye movements were rejected.

Procedure and taskProcedure and task AEPs were submitted to two independent studies:AEPs were submitted to two independent studies:

• 1) a topographic pattern analysis for defining time 1) a topographic pattern analysis for defining time periodsperiods

• 2) instantaneous global field power (GFP) done to 2) instantaneous global field power (GFP) done to minimize observer bias and paired with t-tests minimize observer bias and paired with t-tests

The first point where the t-test exceeded 0.05 The first point where the t-test exceeded 0.05 criterion for 11 consecutive data points was criterion for 11 consecutive data points was labeled as onset of an AEP modulation.labeled as onset of an AEP modulation.

Estimated sources in brain underlying AEPs in Estimated sources in brain underlying AEPs in response to the sounds using local autoregressive response to the sounds using local autoregressive average (LAURA).average (LAURA).

ResultsResults Behavioral:Behavioral:

Subjects performed task with no significant difference Subjects performed task with no significant difference between sensitivity measures based on signal detection between sensitivity measures based on signal detection theory when sounds served as targets.theory when sounds served as targets.

Reaction times did not differ Reaction times did not differ

Time-frequency analysis showed significant living vs. man-Time-frequency analysis showed significant living vs. man-made differences only after ~125ms, no differences made differences only after ~125ms, no differences between mean harmonics to noise ratio indicating they between mean harmonics to noise ratio indicating they cannot account for AEP effects before ~125ms. cannot account for AEP effects before ~125ms.

ResultsResults Electrophysiological:Electrophysiological: Topographic pattern analysis determined whether different configurations of brain Topographic pattern analysis determined whether different configurations of brain

generates accounted for responses to the sounds (7 different topographies). generates accounted for responses to the sounds (7 different topographies).

In the two experimental conditions identical electric field topographies were shown at In the two experimental conditions identical electric field topographies were shown at 0-69, 70-119, 120-154, 258-355, 356-500ms.0-69, 70-119, 120-154, 258-355, 356-500ms.

Two topographies at 155-257ms.Two topographies at 155-257ms.

Neither effect reached 0.05 significance. Neither effect reached 0.05 significance.

Differences in period over N1 component at frontocentral scalp.Differences in period over N1 component at frontocentral scalp.

Tested using 4 electrodes ( AFz, FCz, CPz, POz ).Tested using 4 electrodes ( AFz, FCz, CPz, POz ).

Larger response to man-made sounds only at electrode FCz and over 70-119ms Larger response to man-made sounds only at electrode FCz and over 70-119ms period. period.

155-257ms revealed significant differences with man-made having peaked ~12ms 155-257ms revealed significant differences with man-made having peaked ~12ms earlier.earlier.

ResultsResults LAURA estimations reveal stronger responses to man-made LAURA estimations reveal stronger responses to man-made

sounds in right posterior temporal cortex.sounds in right posterior temporal cortex.

Because differences in electrical fields predominated AEPs Because differences in electrical fields predominated AEPs estimations were calculated for specific periods:estimations were calculated for specific periods:

• Living 155-211 and 212-257msLiving 155-211 and 212-257ms

• Man-made 155-199 and 200-257ms.Man-made 155-199 and 200-257ms.

Both bilateral sources within posterior portion of superior Both bilateral sources within posterior portion of superior and middle temporal cortices and premotor cortices with and middle temporal cortices and premotor cortices with weaker activity in left inferior frontal cortex.weaker activity in left inferior frontal cortex.

Stronger in premotor in response to man-made.Stronger in premotor in response to man-made.

living

Man-made

155-211ms212-257ms

155-199ms 200-257ms

LAURA SOURCE ESTIMATIONS

Discussion/ ConclusionDiscussion/ Conclusion Not linked to behavioural differences, time-frequency, or Not linked to behavioural differences, time-frequency, or

harmonics-to-noise ratios.harmonics-to-noise ratios.

Common network of brain areas involved in auditory what Common network of brain areas involved in auditory what pathway, response more strongly to man-made objects in pathway, response more strongly to man-made objects in regions of right posterior, superior and middle temporal regions of right posterior, superior and middle temporal cortices and left inferior frontal cortex.cortices and left inferior frontal cortex.

Differential processing of categories of sound initiates Differential processing of categories of sound initiates predominantly in strucures of the right hemisphere predominantly in strucures of the right hemisphere

The contrast of animals vs. tools yielded stronger responses The contrast of animals vs. tools yielded stronger responses with middle superior temporal gyruswith middle superior temporal gyrus

Stronger differentiation in tools because they might include Stronger differentiation in tools because they might include richer multisensory and action related associations.richer multisensory and action related associations.

Cheryl Bush Cheryl Bush Cognitive Neuroscience 3680NCognitive Neuroscience 3680N