Image coding using robust quantization for noisy digital transmission.

A robust quantizer is developed for encoding memoryless sources and transmission over the binary symmetric channel (BSC). The system combines channel optimized scalar quantization (COSQ) with all-pass filtering, the latter performed using a binary phase-scrambling/descrambling method. Applied to a broad class of sources, the robust quantizer achieves the same performance as the Gaussian COSQ for the memoryless Gaussian source. This quantizer is used in image coding for transmission over a BSC. The peak signal-to-noise ratio (PSNR) performance degrades gracefully as the channel bit error rate increases.

Disruption of latent inhibition in the rat by the 5-HT2 agonist DOI: effects of MDL 100,907, clozapine, risperidone and haloperidol.

Latent inhibition (LI), a measure of the ability to learn to ignore irrelevant stimuli, is disrupted in acute schizophrenics and in rats treated with amphetamine; antipsychotics prevent amphetamine disruption of LI in rats. The 5-HT2A/C agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) has hallucinogenic properties in humans, and evidence suggests that 5-HT2 antagonism is an important component of atypical antipsychotic activity. Therefore, the ability of DOI to disrupt LI in rats was tested, and the ability of clinically-used and putative antipsychotics to reverse DOI disruption of LI was assessed. The method consisted of four phases. After habituation to the apparatus, thirsty rats underwent preexposure to a tone stimulus 24 h prior to two tone-shock conditioning trials. LI was demonstrated at testing (an additional 24 h later) by reduced lick suppression during tone presentation. When administered at the preexposure phase only, DOI disrupted LI. However, when administered at both preexposure and conditioning phases, DOI did not disrupt LI except at the highest dose, where lick suppression itself was also disrupted. Therefore, disruptive effects of DOI on LI are not easily dissociated from state-dependent learning effects. Additional experiments demonstrated that haloperidol, clozapine, risperidone, and the selective 5-HT2A antagonist MDL 100,907 prevented the disruptive effects of DOI on LI when administered at preexposure only. These results agree with findings that these compounds can also prevent other behavioral effects of DOI. Further experiments will be required to explore the possible involvement of state-dependent learning effects in the present results. However, if the disruptive effects of DOI on LI are due to an influence on attentional processes rather than state-dependent learning, this procedure may have potential as a method for detection of antipsychotic activity.

Comparison of different methods of classification in subband coding of images.

This paper investigates various classification techniques, applied to subband coding of images, as a way of exploiting the nonstationary nature of image subbands. The advantages of subband classification are characterized in a rate-distortion framework in terms of "classification gain" and overall "subband classification gain." Two algorithms, maximum classification gain and equal mean-normalized standard deviation classification, which allow unequal number of blocks in each class, are presented. The dependence between the classification maps from different subbands is exploited either directly while encoding the classification maps or indirectly by constraining the classification maps. The trade-off between the classification gain and the amount of side information is explored. Coding results for a subband image coder based on classification are presented. The simulation results demonstrate the value of classification in subband coding.

Effects of clozapine on latent inhibition in the rat.

In the present study we have examined the effect of clozapine, an atypical antipsychotic drug, on latent inhibition (LI) using the conditioned emotional response (CER) procedure. In this procedure, ten pre-exposures to the to-be-conditioned stimulus result in weak or no LI whereas 30 pre-exposures produce robust LI. Three different experimental protocols were used to study the effects of clozapine: facilitation of LI in animals subjected to ten pre-exposures to the to-be-conditioned stimulus; antagonism of the disruptive effect of amphetamine (1mg/kg, s.c.) on LI in animals receiving 30 pre-exposures; antagonism of the disruptive effect of nicotine (0.6mg/kg, s.c.) on LI in animals receiving 30 pre-exposures. High doses of clozapine (3 and 10mg/kg, s.c.) disrupted the CER in non pre-exposed animals. Despite this, clozapine significantly facilitated the development of LI at 1 and 10mg/kg and significantly attenuated the disruptive effects of nicotine at 0.3 and 1mg/kg and of amphetamine at 2 and 5mg/kg. These results demonstrate that clozapine is active in the LI model and further support the utility of this model in the study of mechanisms of action of antipsychotic drugs.

An entropy-coded lattice vector quantizer for transform and subband image coding.

A lattice-based vector quantizer (VQ) and noiseless code are proposed for transform and subband image coding. The quantization is simple to implement, and no vector codebooks need to be stored. The noiseless code enumerates lattice codevectors based on their (weighted) l(1) norm. A software implementation is able to handle lattice codebooks of size 2(256). The image coding performance is shown to be comparable or superior to the best encoding methods reported in the literature.

On the modeling of DCT and subband image data for compression.

Image subband and discrete cosine transform coefficients are modeled for efficient quantization and noiseless coding. Quantizers and codes are selected based on Laplacian, fixed generalized Gaussian, and adaptive generalized Gaussian models. The quantizers and codes based on the adaptive generalized Gaussian models are always superior in mean-squared error distortion performance but, generally, by no more than 0.08 bit/pixel, compared with the much simpler Laplacian model-based quantizers and noiseless codes. This provides strong motivation for the selection of pyramid codes for transform and subband image coding.