Sound localisation

Question 1

Lord Rayleigh (1907)

Answer 1

Duplex theory of sound Low ITD high ILD

Question 2

Rice et al (1992):

Answer 2

Placed microphone in cat’s ear canal and produced Fast Fourier transforms and found spectral notches exhibit changes with azimuth and elevation location and mapping produces diagonal iso-contour lines which could be disambiguated with the rest of rest of the spectral pattern and first notch od contralateral ear.
o First notch limited to frontal field

Question 3

• May (2000):

Answer 3

Found that lesioning the DCN pathway to the IC in cats found deficits for sound localisation, especially for elevation
o Deficits are only significant with bilateral indicating potentially some compensation
o Lesions to the IAS so damage also to the ascending and descending pathways of the PCVN.

Question 4

• Huang and May (1996):

Answer 4

): Manipulating the frequency and bandwidth orientation of stimuli in sound localisation task in cats demonstrated that best performance was when contained mid-freq bandwidths to convey spectral notches
o Didn’t record responses to the DCN

Question 5

• Irvine et al (2001):

Answer 5

Electrode recoding of LSO in rats in response to different ILDs that some neurons were sensitive to the differences in input times and some in relative amplitues suggest that both contribute to sensitivity of ILDs

Question 6

Joris et al 1998

Answer 6

In a microelectrode study in cats found that responses in TB axons exhibited enhanced synchronisation to AN fibres compared to AN (fibres)

Question 7

Jeffress (1948)

Answer 7

Coincidence detection and delayed lines. Map of ITDs

Question 8

Carr and Konoshi (1990)

Answer 8

Microelectrode recording in nucleus laminaris of barn owl, found that there was systematic variation in preferred ITDs, that cells were frequency selective and phase lock to both monaural and phase lock to monaural and binaural stimuli. They responded most when binaural of preferred ITDs and showed that magnocellular afferents worked as delay lines

Question 9

Brandt et al (2002)

Answer 9

Microelectrode recording of MSO neurons in anaesthetised gerbils using Stychien showed that there was a significant shift in the ITD toward 0ITD, suggesting that glycinergic inhibition via the MNTB and LNTB onto MSO neurons may be responsible for the tuning the steep slope of the ITD curve onto the physiological range of response
o No behavioural

Question 10

• Harper and McAlpine (2004):

Answer 10

emonstrating that the optimal coding strategy for ITD depends critically on head size and sound frequency using statistical techniques and stochastic neural model. Suggest that for small head sizes/ and low freq sounds tends towards distinct sub-populations tuned to ITDs outside the range create by head whereas for large and high, optimal strategy would be for homogenous ITD tuning with range created by head.

Question 11

• Chase and Young (2008):

Answer 11

Used virtual space stimuli and recorded responses of individual neurons of cat IC and found that ITDs represented by firing rate of neurons whereas onset latencies and temporal discharge patterns of AP make larger contribution to the coding of ILDs and spectral notches suggesting a way of combining different sources of information about the direction of sound source whilst preserving independent representations for the cues
o Focuses on first-spike latency

Question 12

Knudsen (1982)

Answer 12

Found that in optic tectum of barn owls that most units responded to auditory and visual information, with both represented topographically. Both had the same orientations, positions and magnitude factors suggesting that the spatio-organisation of the different modalities are aligned.

Question 13

Hartline et al (1995)

Answer 13

Monitoring the eye positions and pinna positions in head-fixed cats and recording visual neurons in the deep layers of the SC and found preferred sound directions of some neurons exhibited a shift with the direction of gaze whilst I others the response throughout the auditory RF was inc/dec suggesting the change in eye position alter the gain in auditory reponses

Question 14

Jenkins and Merzenich (1984)

Answer 14

): Lesioning restricted frequency bands of cat AE resulted in disrupted sound localisation to sound frequencies presented in that area suggesting that sound localisation occurs in a frequency dependant manner

Question 15

• Lee and Middlebrooks (2011)

Answer 15

trained cats of a periodicity detection test and sound location test both requiring active listening and found that spatial tuning of many A1 neurons during active listening narrowed which is likely to be due to inhibitory mechanisms as seemed there was suppression to locations away from the preferred but no change in response of the preferred location

Question 16

• Middlebrooks et al (1994):

Answer 16

Recording from single neurons in cat A1 and used an artificial neural network to classify the temporal spike patterns of single neurons according to sound location and found that the majority of neurons could encode sound location with more than twice the chance level if accuracy and these neurons seem to encode sound locations throughout the 360 deg of azimuth.

Question 17

• Stecker et al (2005)

Answer 17

Microelectrode recording from single units in A1, PAF and DZ to broadband noise at different azimuths. Cortical RFs have broad tuning curve and do not accord to behaviour, but steepest parts of slope of rate-azimuth functions over the interaural midline so proposed an opponent theory of coding in the auditory cortex based on the relative difference in response rates of 2 broadly tuned ipsilateral ad contralateral neurons within each hemisphere. This would provide a response that was frequency and level invariant
o Unilateral lesions. DZ and PAF higher sensitivity to sound localisation,

Question 18

Malhorta and lomber (2008)

Answer 18

Using cooling loops to reversible deactivate bilateral PAF and AAF and found that PAF was implicated in sound localisation whilst AAF was implicated in pattern discrimination suggesting double dissociation between the ventral wat and dorsal where.
o Only looked at 2 brain regions

Question 19

• Keating et al (2015):

Answer 19

Found that adding ear plug (abnormal binaural cues) in adult ferrets made a lot of errors with sound localisation with high-freq narrowband sound cues in different azimuth locations whereas for mice that had an ear plugged since they were juvenile made a lot less errors. Recording A1 neurons to measure ILD sensitivity found there was a mean shift in the ILD in both hemispheres towards the unplugged ear suggesting that A1 can adapt its representation to abnormal binaural cues

Question 20

McAlpine et al (2001)

Answer 20

Recording from the IC of anaesthetised guineapigs to ID broadband noise and estimating sensitivities of ITDs as a function of neuronal BF and NDFs. NDFs showed that responses peaked outside of the physiological range by 150-300μs and the representation varied along tonotopic map with lowest BFs having highest ITD values and higher BFs were narrower and steeper. Steepest part was close to the 0ITD so suggest that there is a rate code. Suggests that ITDs vary across tonotopic map and not within each frequency band with strong relationship between best frequency and ITD
o Not in the MSO