More on Recursion…

Nick Baumann

Katherine Tech

….with Starlings

Background

Recursion is uniquely human

Humans have:• Context-Free Grammar (CFG)

Animals have:• Finite-State Grammar (FSG)

Experiment Apparatus

Ports have IR receiver and transmitter

Holes allowed probing

A hopper provided food

One station per animal for training

Shaping & Selection

Center hole flashing LED = food Initiation of Experiment Learning baseline FSG/CFG

• Only fast learners were used (green)• The others were dinner “The rate of

acquisition varied widely among the starlings that learned the task and was slow by comparison to other song-recognition tasks.”

Conditions

From a single adult male starling

A= Rattles B= Warbles

Context-Free GrammarA2B2

Finite-State Grammar (AB)2

Results

Nine of the eleven birds able to classify FSG and CFG sequences

Have the capacity to describe long strings – generative grammar Baseline of n=2Probed birds with n=3, n=4

Further tests done to ensure proper interpretation of data

Some Possibilities…

Classified patterns described by CFG/FSG grammars throughRote Memorization of training examplesLearn only FSG and CFG is the

complement setListening for

• A/B and B/A transitions• BB, AA, and AB motif pairs

Rote Memorization Testing

Transferred birds abruptly from the training stimuli to new sequences Baseline: n =2 Example: New CFG: AAAAAABBBBBB New FSG: ABABABABA

Starlings correctly classified the new CFG and FSG sequences Acquired general knowledge characteristic of the two grammars Birds did not memorize the training stimuli

CFG as a complement set

Made 16 new sequences based on 4 agrammatical patterns

Agrammatical Patterns: AAAA, ABBA, BBBB, and BAAB

Presented among grammatical sequences “The response patterns for the agrammatical probe

stimuli differed significantly from those for new (AB)2 stimuli for all four birds, and from those for new A2B2

stimuli for three of the four birds”

Listening for pairs and transitions

Classifying sequences by pairs at the start or end Ex. xxAB xxBB and AAxx ABxx

Counting A/B and B/A Transitions

Test possibility with agrammatical stimuli End: response times similar between AAAB and

BBBB and their counterpart (AB) 2 and A2B2

Transitions: discriminate between ABBA, BAAB, AAAA and BBBB and similar times with reference

Is Recursion Important?

More to speech than recursionPeople can still speak without itPremack 2004

• Voluntary control of sensory-motor systems

• Imitation/Teaching • Theory of the Mind• Vocabulary

Recursion in Humans

Marcus 2006Humans have better ability for

recursion

• No extensive training

• Generalize recursion to new words

Are Conclusions Valid?

Is it possible for finite-state grammar to mimic context-free grammar?Pattern recognition could lead to same

result Humans fail similar tests

The cats the dog the men walk chases run away.

Continued…

Perruchet and Rey 2004 “We report an experiment replicating the

results of F&H in humans, but also showing that participants learned the language without exploiting in any way the center-embedded structure. When the procedure was modified to make the processing of this structure mandatory, participants no longer showed evidence of learning.”