Disparity in interaural time difference improves the accuracy of neural representations of individual concurrent narrowband sounds in rat inferior colliculus and auditory cortex

The central mechanisms underlying binaural unmasking for spectrally overlapping concurrent sounds, which are unresolved in the peripheral auditory system, remain largely unknown. In this study, frequency-following responses (FFRs) to two binaurally presented independent narrowband noises (NBNs) with overlapping spectra were recorded simultaneously in the inferior colliculus (IC) and auditory cortex (AC) in anesthetized rats. The results showed that for both IC FFRs and AC FFRs, introducing an interaural time difference (ITD) disparity between the two concurrent NBNs enhanced the representation fidelity, reflected by the increased coherence between the responses evoked by double-NBN stimulation and the responses evoked by single NBNs. The ITD disparity effect varied across frequency bands, being more marked for higher frequency bands in the IC and lower frequency bands in the AC. Moreover, the coherence between IC responses and AC responses was also enhanced by the ITD disparity, and the enhancement was most prominent for low-frequency bands and the IC and the AC on the same side. These results suggest a critical role of the ITD cue in the neural segregation of spectrotemporally overlapping sounds. NEW & NOTEWORTHY When two spectrally overlapped narrowband noises are presented at the same time with the same sound-pressure level, they mask each other. Introducing a disparity in interaural time difference between these two narrowband noises improves the accuracy of the neural representation of individual sounds in both the inferior colliculus and the auditory cortex. The lower frequency signal transformation from the inferior colliculus to the auditory cortex on the same side is also enhanced, showing the effect of binaural unmasking.

Perceptual dimensions of style in paintings

The main purpose of this study is to specify the basic perceptual dimensions underlying the judgments of the physical features which define the style in paintings (e.g. salient form, colorful surface, oval contours etc.). The other aim of the study is to correlate these dimensions with the subjective (affective) dimensions of the experience of paintings. In the preliminary study a set of 25 pairs of elementary perceptual descriptors were empirically specified, and a set of 25 bipolar scales were made (e.g. uncolored-multicolored). In the experiment 30 subjects judged 24 paintings (paintings were taken from the study of Radonjic and Markovic, 2004) on 25 scales. Factor analysis revealed the four factors: form (scales: precise, neat, salient form etc.), color (color contrast, lightness contrast, vivid colors), space (voluminosity, depth and oval contours) and complexity (multicolored, ornate, detailed). Obtained factors reflected the nature of the phenomenological and neural segregation of form, color, depth processing, and partially of complexity processing (e.g. spatial frequency processing within both the form and color subsystem). The aim of the next step of analysis was to specify the correlations between two groups of judgments: (a) mean judgments of 24 paintings on perceptual factors and (b) mean judgments of the same set of 24 paintings on subjective (affective) experience factors, i.e. regularity, attraction, arousal and relaxation (judgments taken from Radonjic and Markovic, 2005). The following significant correlations were obtained: regularity-form, regularity-space, attraction-form and arousal-complexity (negative correlation). The reasons for the unexpected negative correlation between arousal and complexity should be specified in further studies.

One visual system with two interacting visual streams

Norman's aim to reconcile two longstanding and seemingly opposed philosophies of perception, the constructivist and the ecological, by casting them as approaches to complementary subsystems within the visual brain is laudable. Unfortunately, Norman overreaches in attempting to equate direct perception with dorsal/unconscious visual processing and indirect perception with ventral/conscious visual processing. Even a cursory review suggests that the functional and neural segregation of direct and indirect perception is not as clear as the target article would suggest.