Complex Sound Discrimination Abilities in Rats and the Effects of Multiple Training Manipulations A. C. Puckett, C. T. Novitski, N. D. Engineer, A. L. Mc. Menamy, M. S. Perry, C. A. Perez, P. Kan, Y. H. Chen, V. Jakkamsetti, C. L. Heydrick, M. P. Kilgard, The University of Texas at Dallas, Richardson, TX SEQUENCE DISCRIMINATION SPEECH DISCRIMINATION Introduction Speech Stimulus Creation The current experiments have examined the ability of rats to perform discriminations among complex sounds, including tone-noise sequences and speech stimuli. Understanding how normal animals are able to discriminate complex sounds is necessary in order to fully understand the auditory cortex and how injury, learning or plasticity can change perception and cortical functioning. n. s. • Recording: Monosyllabic words spoken by female native English speaker in a sound-proof chamber. –The words ‘dad’ and ‘tad’ were recorded from 5 other native English speakers (3 male, 2 female) to assess speaker generalization. • Frequency shifting: The frequency of the fundamental and all other formants were shifted into the rat’s hearing range by doubling their frequency. –Compressed versions of ‘dad’ and ‘tad’ were generated to assess temporal generalization. • Noise reduction: Background noise was subtracted from each signal. • Filtering: Each signal was filtered to correct for the frequency-response curve of the booth speaker. • Intensity adjustment: The RMS-values of the signals were adjusted so that the loudest 100 ms of each vowel was 60 d. B SPL. Behavioral data was collected from 46 rats over 4661 total daily training sessions. n. s. Methods All animals performed Go/ No-Go discrimination tasks in the same operant training booths. The stimuli used as CS+ and CS- varied among different training tasks, but the general timeline of training and procedures were the same for all tasks. Apparatus Dad Tad • Sounds are delivered from a speaker placed outside the cage. Speaker is positioned so that sounds are usually delivered to the animal’s left ear. • L – Rat responds to sound stimuli by pressing on the lever. Only presses within 3 seconds of CS+ stimuli are rewarded. • P – Pellet dispenser (MED Associates) located outside the sound-proof chamber delivers a 45 mg food reward (Bio-Serv) to the rat after correct responses. • H – House light is extinguished after false alarms or late responses n. s. HLN NLH Rad Lad Conclusions Shaping Goal: Animals learn to press lever to receive food rewards Time Course: ~ 6 sessions (3 days). Continued until 3 sessions in which animals retrieved 50 pellets independently. Detection Training Goal: Animals learn to press to receive rewards only after they hear a sound. Animals must learn to avoid hitting during silent periods. Time course: ~30 sessions (3 weeks). Continued until 10 sessions in which animals respond significantly more to CS+ trials than to catch trials (ie, d’ >= 1. 5 for 10 sessions) Conclusions • Frequency discriminations are easy, but other sequence discriminations are difficult. • Onsets are the most salient elements of sequences. • Sequences beginning with the same element are difficult to discriminate. • Reversed sequence discrimination was impossible, despite different initial elements. • Sequences may be normally processed as a ‘unit’ rather than discrete elements. • Discrimination strategies may be changed by training. • If rats learn a poor strategy early in training, they will not learn to discriminate effectively. • Intermediate exemplars allowed animals to adopt effective strategies. Stages of Training Discrimination Training Goal: Animals learn to press to receive rewards only after they hear a CS+. Animals must avoid hitting after CS- stimuli or during silent periods. Time course: Variable (20 – 300 sessions). Sequence Discrimination: Animals trained for up to 300 sessions or until behavioral criteria were met. Speech Discrimination: Animals progressed through a variety of CS- conditions after 2 weeks of training on each task, regardless of behavioral performance. n. s. • Large spectral differences are easy for rats to discriminate, even if differences are not in the onset of the speech sound. • Onsets/consonants: /dad/ vs. /bad/ & /gad/ • Middle of stimulus/vowels: /dad/ vs. /deed/ & /dood/ • Subtle spectral differences are difficult for rats to discriminate (and are difficult for humans as well). • Onsets/consonants: /rad/ vs. /lad/ • Middle of stimulus/vowels: /dad/ vs. /dead/ & /dud/ • Rats can generalize among several variants of a speech stimulus. • Rats could generalize across several compressed exemplars, indicating that VOT wasn’t the only cue. • Rats could generalize across several different speakers. Rats were able to generalize across many different fundamental frequencies, temporal patterns of enunciation, and other idiosyncrasies. • Speech sounds seem to be more easily discriminated than tone-noise sequences. HLN vs. Future Directions – www. utd. edu/~kilgard • • • Assessment of changes in perceptual abilities after NB-stimulation pairing Measurement of changes in auditory cortex after long-term sequence training Measurement of responses of auditory cortex after long-term speech training Assessment of cortical processing of speech sounds after environmental enrichment Assessment of loss of perceptual abilities after cortical injury Information theory analysis of cortical responses to speech sounds Amanda Puckett Dr. Navzer Engineer Crystal Novitski Vikram Jakkamsetti Dr. Owen Floody Helen Chen dad vs. In Loving Memory of Matt Perry (March 1981 - September 2005) In honor of the neuroscientist who delved into the mysteries and whims of life with wholehearted delight. Thank you to one who touched the minds he sought to understand. As a true inquirer into philosophy, pharmacology and literature, Mat enriched rats as well as people. It is an honor to have shared a common path with you. Acknowledgements We wish to thank all the members of the Kilgard Lab behavioral team. Research supported by NIH R 21#1 R 15 DC 00662401
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