Notes for week 6

Barbara

Shimon

Yu & Margoliash

• "Motor activity in the zebra finch HVc is centered on the syllable, is based on syllable type, and is independent of syllable context."
• "In contrast to the relatively tonic discharge patterns of HVc neurons, neuronal activity in the RA during singing was characterized by trains of short bursts of spikes separated by periods of profound inhibition. [...] Each spike burst was characterized by a stereotyped and unique pattern of intraburst timing. The reliability of activity patterns was sufficient to allow correct inference of vocal output from individual spike trains."
• "The pattern of activity of HVc neurons associated with each note depends in part on the identity (type) of the syllable in which the note is embedded."
• "These data imply a hierarchical organization for the forebrain control of bird song production."

Drew & Abbott

• Simulation of field L is trivial (a bank of STRF filters).
• "The syllable- and temporal-combination- selective units in our model are integrate-and-fire neurons driven by the field L outputs. Individual syllable-selective units receive excitatory synaptic conductances proportional to a weighted sum of the firing rates of the field L units. Syllable selectivity arises from an appropriate choice of the weights in this sum, with each weight corresponding to a unitary synaptic conductance."
• "Not all syllables were recognizable by our model. It was easiest to select for syllables with power tightly concentrated at one or a few frequencies, such as whistles and harmonic stacks. Syllables with broadly distributed power generated weaker responses and more false positive responses to incorrect syllables."
• "The critical feature that must be added to expand and extend syllable-selectivity to temporal-combination selectivity is a memory trace of the sequence being selected that can gate the response. Figure 5 shows a schematic of the network we used to generate temporal-combination-selective responses." [Why not use a polychronous chain to generate / respond to syllable components in the proper order??]

Dominey

• "A fundamental aspect of sequential structure is serial order. From this perspective, sequences ABC and ACB are distinct. A second level of sequential organization is temporal or rhythmic structure. From this perspective, A-BC and AB-C are distinct. The final level of organization that we will consider has to do with the potential relation between two sequences such as ABCBAC and DEFEDF."
• "[DLPFC] visual-tonic neurons encoded both the spatial location of a given target, along with its rank within the sequence. Thus, a given neuron might represent the left target but only when it was first (and not second or last) in the sequence."
• Dominey's PFC / striatum model (Temporal Recurrent Network, TRN) is almost exactly like Elman's SRN.
• An elaboration: Abstract Temporal Recurrent Network (ATRN), in which the sequence is first preprocessed to detect self-matching elements and is recoded accordingly.
• Equivalence hypothesis: "the same neural systems invoked by the processing of nonlinguistic behavioral sequences that possess the appropriate degree of abstract structure are also responsible for the thematic role processing" [as in who did what to whom]. Model: Fig.3.