AUDITORY LATE RESPONSE

1. Stimulus types:

1.1. Tone burst

1.2. speech material such as \pa\ da\

1.3. clicks-not generally used

1.4. whole words (synonyms and antonyms) | usually occurs at late negative peaks N400

2. effects of the stimulus type on the overall responses:

2.1. 1- Low frequency --> late & large amplitude (N1 & P2)

2.2. 2- "processing negativity" peak occurs with only one frequency stimulus between 70-700 ms

2.3. 3- Using complex tones --> larger amplitude

2.4. 4- Using speech stimuli --> larger amplitude + later latency especially N1 &P2

2.5. 5- Speech stimuli --> larger amplitude in left hemisphere recording channel

2.6. 6- Tonal stimuli --> larger amplitude in right hemisphere recording channel.

3. Stimulus characteristic:

3.1. Duration: around 60-70 ms & 10 s for rise\fall | using short rise\fall ( less than 3-4 ms --> reduces ALR amplitude significantly)

3.2. Intensity: * Higher intensity --> larger amplitude and shorter latencies. * usually 60-70 dB HL *the amplitude of ALR is usually larger than other potentials ( ranges b.w 3-10 microvolt)

3.3. Rate: very slow rate - usually 0.7 to 1.7\sec

3.4. Contralateral competing presentation: leads to decrease in N1 amplitude | bilateral stimulation is negligible (insignificant) compared to Unilateral.

3.5. Recording parameters:

3.5.1. analysis time--> long 500-700 ms

3.5.2. sweeps -->15 to 50

3.5.3. filters --> 0.1 -100 Hz

3.5.4. Sites : 1) inverting -> earlobe.mastoid or nape of neck 2)Non-inverting --> Fz,Cz 3) Ground --> Fpz

4. effects of subject variables on ALR:

4.1. Age: generally, the waveform completed around 4-5 months | highest at 6 to 15 yrs.

4.2. Attention: increases the amplitude

4.3. Gender : 1) recording form the LH --> larger in female 2) recording from the RH 00> larger in male

4.4. Handedness : left handed has shorter N1 latency and smaller P2 amplitude

4.5. state of arousal( sleeping has great effect on ALR ) : 1) Shallow sleep --> ALR amplitude decrease while latency increase 2) sleeping --> N1 amplitude decrease while P2 amplitude increase

4.6. Auditory training : better discrimination and larger amplitude of N1 & P2

4.7. Drugs: affects ALR such as alcohol,sedative

5. Clinical applications:

5.1. 1) hearing estimation for infants and FHL

5.2. 2) objective threshold estimation for adult

5.3. 3) Identify pathology of higher auditory processing

5.4. 4) used in many cases to study auditory processing disorder

5.5. 5) smaller amplitude of N1 for individuals with Auditory Processing Disorders and have problem processing auditory signals with background noise

5.6. 6) Test higher auditory processing

5.7. 7)Down syndrome : has larger amplitude

5.8. Tinnitus --> steeper amplitude as freq match the tinnitus

5.9. Hyperacusis --> steeper as intensity increase

5.10. other applications: depression, head injury, schizophrenia , learning and language delay

6. Definition

6.1. associated with electrophysiological records of the auditory system (AEPs)

7. Characteristics:

7.1. 1- Arises for cerebral cortex

7.2. 2- subject has to pay attention

7.3. 3- test higher level of auditory system than ABR

8. Waveforms: