Putting the tritone paradox into context: insights from neural population decoding and human psychophysics.

The context in which a stimulus occurs can influence its perception. We study contextual effects in audition using the tritone paradox, where a pair of complex (Shepard) tones separated by half an octave can be perceived as ascending or descending. While ambiguous in isolation, they are heard with a clear upward or downward change in pitch, when preceded by spectrally matched biasing sequences. We presented these biased Shepard pairs to awake ferrets and obtained neuronal responses from primary auditory cortex. Using dimensionality reduction from the neural population response, we decode the perceived pitch for each tone. The bias sequence is found to reliably shift the perceived pitch of the tones away from its central frequency. Using human psychophysics, we provide evidence that this shift in pitch is present in active human perception as well. These results are incompatible with the standard absolute distance decoder for Shepard tones, which would have predicted the bias to attract the tones. We propose a relative decoder that takes the stimulus history into account and is consistent with the present and other data sets.

Streptococcus pneumoniae resistant to penicillin: incidence and potential therapeutic options.

Streptococcus pneumoniae was recovered from 12 (50%) samples of middle ear fluid of 24 consecutive patients with AOME and in mixed culture of middle ear pathogens from one (4%) additional specimen. Two (15.3%) isolates had intermediate resistance to penicillin (minimal inhibitory concentration (MIC) 0.125 and 1.0 micrograms/mL). The antimicrobial susceptibility to various antimicrobials of 30 S pneumoniae strains recovered from patients seen in the last 12 months was also determined. One of the patients with AOME developed bacteremia that resolved uneventfully, whereas the other developed meningitis. MIC90 was determined from penicillin (2 micrograms/mL), erythromycin (> 32 micrograms/mL), cefaclor (32 micrograms/mL), loracarbef (> or = 64 micrograms/mL), cefixime (16 micrograms/mL), ceftibuten (> 64 micrograms/mL), chloramphenicol (16 micrograms/mL), cefpodoxime (4 micrograms/mL), ciprofloxacin (2 micrograms/mL), cephalexin (> or = micrograms/mL), augmentin (2 micrograms/mL), cefprozil (8 micrograms/mL), clindamycin (64 micrograms/mL), TMP-SXT (> 64 micrograms/mL), clarithromycin (32 micrograms/mL), rifampin (0.06 micrograms/mL), cefuroxime (2 micrograms/mL), cefotaxime (0.25 micrograms/mL), vancomycin (0.25 micrograms/mL), and imipenem (0.5 micrograms/mL). Cefprozil, vancomycin, and rifampin inhibited all strains, whereas cefpodoxime, cefuroxime, clindamycin, and clarithromycin exhibited very good activity.