$ studying barn owls in the laboratory $ sound intensity cues $ sound timing cues $ neural pathways for sound location $ auditory space $ interaural time differences $ delay lines & coincidence detectors $ visual calibration of the auditory world $ summary PART 2: SENSORY WORLDS #08: PREY LOCATION IN BARN OWLS II

$ studying barn owls in the laboratory $ sound intensity cues $ sound timing cues $ neural pathways for sound location $ auditory space $ interaural time differences $ delay lines & coincidence detectors $ visual calibration of the auditory world $ summary PART 2: SENSORY WORLDS #08: PREY LOCATION IN BARN OWLS II

$ owls are auditory & visual animals $ systems integrated  locate source of stimulus $ recall experimental set up... VISUAL CALIBRATION OF THE AUDITORY WORLD

$ monitor head orientation behavior $ used “search coil”  weak electric field $ signal magnitude + sign  head position $ ~ sounds $ no echoes $ total darkness $ sound & head positions correlated by computer p.64 fig.3.2 BARN OWLS IN THE LABORATORY

$ monaural occlusion experiments  location error $ elevation $ azimuth (minor) $ 2 critical observations... p.67 fig correction after weeks ? $ young owls  yes $ old owls  less 2. remove occlusion $ error persists, but... $ corrected / time BEHAVIORAL ANALYSIS

$ monaural occlusion experiments  location error $ elevation $ azimuth (minor) p.67 fig.3.4 $ other cues... vision ? $ prisms  correct ~ visual offset BEHAVIORAL ANALYSIS

$ hypothesis: vision guides evaluation of auditory cues $ raised young (sensitive) owls with prisms $ do owls adjust auditory targeting ~ visual input ? $ results: $ normal $ visual shift only $...auditory shift p.83 fig.3.15 $ shift remains VISUAL vs AUDITORY STIMULI

$ developmental regulation of shift $  7 mo, shift ~ 20° $ adults, shift only a few ° $ results: $ normal $ visual shift only $...auditory shift p.83 fig.3.15 $ shift remains VISUAL vs AUDITORY STIMULI

$ convergence: $ azimuthal (ITD) & horizontal (ILD) info in ICX $ auditory & visual information in optic tectum $ receptive fields of optic tectum aligned in columns p.84 fig.3.16 NEURAL CORRELATES OF PLASTICITY

$ receptive fields of optic tectum aligned in columns p.85 fig.3.17 (A) multimodal space map in optic tectum (B) prisms shift visual receptive field (C) + 8 wks... auditory receptive field shifts NEURAL CORRELATES OF PLASTICITY

$ azimuthal plane... expect $ horizontal shift in auditory perceptive fields $ induced by abnormal visual cues $ accompanied by ~ shift in ITDs of tectal neurons p.85 fig.3.17 $ what causes this shift in alignment ? NEURAL CORRELATES OF PLASTICITY

$ adaptation of ITD map ~ visual experience p.86 fig.3.18 (A) optic tectum neurons $ normal  visual 0  s (center of field) $ 8 wks of prism  visual ~ 50  s (B) optic tectum neuron arrays $ shifts follow pattern of visual experience NEURAL CORRELATES OF PLASTICITY

$ ITD tuning curves in ICX neurons of prism-reared owls $ shaded = normal & learned $ 2 stages of ITD adjustment p.87 fig.3.19 (A) initial: az.= 0°, ITD = 0  s (B) transition: az., ITD  (C) shift: az.= 23°, ITD = 40  s NEURAL CORRELATES OF PLASTICITY

$ visual experience modification of auditory localization $ young adult  60 days 200  $ monaural occlusion $ displacement prisms $ optic tectum ITD tuning (A) juveniles: sensitive to prisms (B) adults: naïve – insensitive to prisms (  ) experienced – sensitive (  ) p.88 fig.3.20 SENSITIVE PERIOD FOR CALIBRATION

$ visual horizontal displacement  $ auditory space maps $ optic tectum ITD map $ auditory space maps: ICC  ICX  op.tectum p.90 fig.3.21 SITES OF ADAPTIVE PLASTICITY

$ auditory space maps: ICC  ICX  op.tectum $ prism reared owls: $ ICC map normal $ ICX map shifted ~ optic tectum shift $ anatomy $ normal ICC-ICX input $ additional ICC-ICX input to shifted ITD region $ accounts for recovery during lifetime  normal $ accounts for rapid readjustment  prisms again p.90 fig.3.21 SITES OF ADAPTIVE PLASTICITY

$ cellular mechanisms ? $ involves: $ glutamate - excitatory neurotransmitter $ glutamate receptor - NMDA receptor p.90 fig.3.21 SITES OF ADAPTIVE PLASTICITY

$ experiments identified 2 critical auditory cues... $ time info, ITD  NM  azimuthal information $ intensity info, ILD  NA  elevation information $ parallel processed, cochlear nuclei  ICX $ ITD & ILD information  ICX space-specific neurons $ each neuron  receptive field in auditory space $ emergent / unique property (not signal addition) $ coordinated auditory & visual world $ visual tuning of auditory space $ young / juvenile > adult SUMMARY

$ multimodal maps of sensory world in optic tectum $ auditory maps can shift  register with visual $ young adult $ realignment by new ICC  ICX connections $ connections persistent SUMMARY