novelty-detection-ncm/NCM-errors/description

These experiments were conducted as follows...

SUBJECTS:
Electrophysiological recordings were carried out in 6 adult zebra finches (Taeniopygia guttata) from the
MIT zebra finch breeding facility. Birds ranged from 120-400 days post-hatch in age. 
Craniotomies were performed and headposts implanted on birds in order to prepare birds 
for head-fixation and electrophysiological recordings.


HEAD FIXATION AND E-PHYS RECORDINGS:
In advance of recording, birds were gradually habituated to the recording setup over the course of 3 days.
Neuropixel probes (Phase 3a [Jun et al., 2017]) were used together with OpenEphys software 
(https://open-ephys.org/) for data acquisition, aloing with the PXIe system (National Instrument 
NI-PXIe-1071). Extracellular signals were amplified and filtered (0.3-10 kHz) to obtain action potential 
data. Craniotomies were made so that the center of the cranial aperture was centered above NCM (see 
surgery protocol), and the probe was lowered approximately 2000 𝜇m below the surface of the brain, until 
auditory responses were visible up to the 200th contact from the bottom of the probe (approximately 
1500 𝜇m from the probe tip).

Experiments took place on an optical table, surrounded by a home-made sound- reduction enclosure.


EXPERIMENTAL STRUCTURE:
Two separate experiments were performed. The first experiment was a recapitulation of the classical 
song-specific adaptation experiment [Chew et al., 1995b]. 4 standard songs (with motifs of 4 or 5 
syllables each) were presented to the bird over 2 epochs. During the first epoch, each song was 
presented for 25 bouts of 5 motifs each, with inter-motif intervals of 30ms and inter-bout intervals 
of random length, uniformly distributed between 7 and 13 seconds. After each of the 4 songs was presented 
during the first epoch, songs were repeated (in the same order) during the second epoch, for 10 bouts each.

The second experiment involved 4 distinct epochs, during which 1 standard song (consisting of 5 syllables) 
and 18 variations on that song were presented. The 18 variations were composed of (whole syllable versus 
intra-syllable perturbations), (per- turbations of syllable b, d or e), and (harmonic stack insertions, 
spectrally matched noise insertions, or silence insertions), for a total of (2 x 3 x 3 = 18) distinct 
perturba- tions. During the first epoch (baseline phase 1), each of the 19 different motifs (18 perturbed 
motifs plus 1 standard motif) were presented in a random order, 25 times each. Motifs were separated by a 
random inter-motif interval, uniformly distributed between 0.5 and 1.5 seconds. During the second epoch 
(oddball phase), 3-6 standard motifs (uniformly distributed) were followed by a single perturbed motif, 
with 30ms between motifs. There were 25 such trials for each of the 18 perturbed motifs. During the third 
epoch (habituation phase), the standard motif was presented in 80 bouts of 5 motifs each. Motifs were 
separated by 30ms, and bouts were separated by 2-4 seconds (uniformly distributed). The fourth and final 
epoch (baseline phase 2), was an exact repetition of the first epoch (baseline phase 1).


AUDITORY STIMULATION:
Auditory stimuli were synthesized using custom MATLAB code and stimulus com- ponents from the 
Tchernikovskii lab zebra finch song archive [Tchernichovski et al., 2004], 
http://ofer.sci.ccny.cuny.edu/songs. Perturbations were introduced by inserting harmonic stacks (in the 
case of harmonic stack substitution), eliminating all sound (in the case of silence substitutions), or 
inserting spectrally matched noise (in the case of noise substitution). All substitutions were made using 
cosine-squared ramps to minimize edge artifacts. Spectrally-matched noise was generated by randomizing 
the phase of the standard, unperturbed birdsong. Sound amplitudes were matched so that substitutions 
(aside from silence) were as loud as the standard song piece that they replaced.

Sounds were played through a PyleDriverPro speaker, with SPL of 75 dB at 20 cm. This intensity was 
matched to the sound level of an adult zebra finch singing at the same distance.