Visual ecology: coloured fruit is what the eye sees best

Trichromatic vision may have evolved as an aid to frugivory. This hypothesis is supported by the recent demonstration that the spatial characteristics of pictures containing fruit are particularly well matched to the abilities of the human visual system.     

Measures of human olfactory perception during pregnancy

Although considerable anecdotal evidence suggests that pregnancy affects olfactory sensitivity, scientific evidence is limited and inconclusive. Whereas hedonic ratings are affected by pregnancy, odor identification is not. The aim of the current study was to examine odor perception in women across pregnancy and in the postpartum period. One hundred nonsmoking women who were pregnant, postpartum, or had never been pregnant were tested on the University of Pennsylvania Smell Identification Test (UPSIT). Intensity ratings and scratch patterns were collected as potential indicators of sensitivity, and participants rated the odors' pleasantness. Participants also rated their own sense of smell. Mean UPSIT scores did not differ significantly across groups indicating no difference in odor identification. Trends in planned comparisons suggested that in the first trimester, odors were rated as more intense and less pleasant. In the first trimester, women scratched the odor strips significantly fewer times. Consistent with previous reports, 90% of pregnant women reported that specific odors smelled less pleasant and 60% reported that some odors smelled more pleasant. Although nearly two-thirds of pregnant women rated their olfactory sensitivity to be enhanced during pregnancy and overall pregnant women's self-rated olfactory sensitivity was higher than controls', self-ratings were not correlated with UPSIT scores nor odor intensity ratings. These results suggest that these and previous findings may reflect the fact that the effect of pregnancy on olfaction is small and inconsistent.     

The mechanism of interaction between visual flow and eye velocity signals for heading perception

A translating eye receives a radial pattern of motion that is centered on the direction of heading. If the eye is rotating and translating, visual and extraretinal signals help to cancel the rotation and to perceive heading correctly. This involves (1) an interaction between visual and eye movement signals and (2) a motion template stage that analyzes the pattern of visual motion. Early interaction leads to motion templates that integrate head-centered motion signals in the visual field. Integration of retinal motion signals leads to late interaction. Here, we show that retinal flow limits precision of heading. This result argues against an early, vector subtraction type of interaction, but is consistent with a late, gain field type of interaction with eye velocity signals and neurophysiological findings in area MST of the monkey.     

The physics of visual perception

By measuring the contrast threshold for gratings of different waveform and spatial frequency, Campbell & Robson suggested in 1968 that there may be 'channels' tuned to different spatial frequencies. By using the technique of adapting to a high contrast grating, it was possible to measure the band-pass characteristics of these channels. Similar techniques were used to establish the orientational tuning of the channels. Reasons are put forward why it is advantageous to organize the visual system in this manner.     

Sounds reset rhythms of visual cortex and corresponding human visual perception

An event in one sensory modality can phase reset brain oscillations concerning another modality. In principle, this may result in stimulus-locked periodicity in behavioral performance. Here we considered this possible cross-modal impact of a sound for one of the best-characterized rhythms arising from the visual system, namely occipital alpha-oscillations (8-14 Hz). We presented brief sounds and concurrently recorded electroencephalography (EEG) and/or probed visual cortex excitability (phosphene perception) through occipital transcranial magnetic stimulation (TMS). In a first, TMS-only experiment, phosphene perception rate against time postsound showed a periodic pattern cycling at ~10 Hz phase-aligned to the sound. In a second, combined TMS-EEG experiment, TMS-trials reproduced the cyclical phosphene pattern and revealed a ~10 Hz pattern also for EEG-derived measures of occipital cortex reactivity to the TMS pulses. Crucially, EEG-data from intermingled trials without TMS established cross-modal phase-locking of occipitoparietal alpha oscillations. These independently recorded variables, i.e., occipital cortex excitability and reactivity and EEG phase dynamics, were significantly correlated. This shows that cross-modal phase locking of oscillatory visual cortex activity can arise in the human brain to affect perceptual and EEG measures of visual processing in a cyclical manner, consistent with occipital alpha oscillations underlying a rapid cycling of neural excitability in visual areas.     

Optimization of magnetophoretic-guided drug delivery to the olfactory region in a human nose model

Magnetophoretic-guided delivery has been shown to be able to improve the olfactory doses. However, due to the complex nasal structure and quick decay of magnetic intensity, precise control of particle motion in the human nose remains a challenge. In this study, an optimization model was developed for magnetophoretic olfactory delivery systems. The performance of the model was evaluated using a baseline device design in an MRI-based human nose geometry. Three key components of the delivery system were examined, which included the particle release position, the front magnet to minimize nasal valve depositions, and the top magnet to attract particles into the olfactory region. Results show that the magnetophoretic olfactory delivery device can be significantly improved by optimizing the product and operational parameters. The olfactory delivery efficiency was increased by 1.5-fold compared to the baseline design. The top magnet height and strength were shown to be the most influential factor in olfactory delivery, followed by the drug release position and the front magnet strength. The optimization framework developed in this study can be easily adapted for the optimization of intranasal drug delivery to other regions such as paranasal sinuses.     

Seeing what the mouse sees with its vibrissae: a matter of behavioral state

The behavioral state of an animal is accompanied by ongoing brain activity that primes neuronal circuitry to sensory inputs. While it should come as no surprise that the pattern of cortical activation is tied to behavioral states, only now has this dependence been imaged. In this issue of Neuron, Ferezou, Bolea, and Petersen show that the level and spatial extent of activation of vibrissa sensory cortex critically depend on behavioral context and mode of stimulation, i.e., passive versus active contact.     

Confusing tastes and smells: how odours can influence the perception of sweet and sour tastes

This study investigated the relationship between perception of an odour when smelled and the taste of a solution to which the odour is added as a flavorant. In Experiment 1 (E1) sweetness, sourness, liking and intensity ratings were obtained for 20 odours. Taste ratings were then obtained for sucrose solutions to which the odours had been added as flavorants. Certain odours were found to enhance tasted sweetness while others suppressed it. The degree to which an odour smelled sweet was the best predictor of the taste ratings. These findings were extended in Experiment 2 (E2), which included a second tastant, citric acid, and employed four odours from E1. The most sweet smelling odour, caramel, was found to suppress the sourness of citric acid and, as in E1, to enhance the sweetness of sucrose. Again, odours with low sweetness suppressed the sweetness of tasted sucrose. The study demonstrated that the effects of odours on taste perception are not limited to sweetness enhancement and apply to sour as well as sweet tastes. The overall pattern of results is consistent with an explanation of the taste properties of odours in terms of prior flavour-taste associations.     

The perception of visual motion.

Recent developments have led to a greater insight into the complex processes of perception of visual motion. A better understanding of the neuronal circuitry involved and advances in electrophysiological techniques have allowed researchers to alter the perception of an animal with a stimulating electrode. In addition, studies have further elucidated the processes by which signals are combined and compared, allowing a greater understanding of the effects of selective brain damage.     

Distortion of olfactory perception: diagnosis and treatment

Clinically, olfaction can fail in any of three ways: (i) decreased sensitivity (hyposmia, anosmia) and two types of distortion (dysosmia); (ii) distorted quality of an odorant stimulation (troposmia); (iii) perceived odor when no odorant is present (phantosmia, hallucination). The distortions are usually much more upsetting to a person's quality of life than a simple loss. An ipsilatersal loss of olfactory sensitivity is often identified in the nostril with any type of olfactory distortion. The pathophysiology of a stimulated distortion (troposmia) is likely a decreased number of functioning olfactory primary neurons so that an incomplete characterization of the odorant is made. In phantosmia, two possible causations include an abnormal signal or inhibition from the primary olfactory neurons or peripheral olfactory or trigeminal signals that "trigger" a central process. The clinician's goal is to carefully define the problem (e.g. taste versus smell, real versus perceived, one versus two nostrils), to perform the appropriate examination and testing and to provide therapy if possible. Treatment includes assurance with no active therapy (because many of these will naturally resolve), topical medications, systemic medications, anesthesia to parts of the nose and, rarely, referral for surgical excision of olfactory neurons. Endoscopic transnasal operations have the advantage of treating phantosmia and sometimes allowing a return of olfactory ability after the operation.     

The salamander nose: a model system for the study of spatial coding of olfactory quality

Recent experiments in the salamander on the spatial coding ofodorant quality have revealed that different odorants elicitdifferent topographic patterns of olfactory receptor cell responseswhich are independent of odorant concentration. These experimentsfrom the laboratory of David Moulton confirm and extend ideasexpressed in his recent review (Moulton, 1976).     

Visual perception: more than meets the eye

A recent study shows that objects changing in colour, luminance, size or shape appear to stop changing when they move. These and other compelling illusions provide tantalizing clues about the mechanisms and limitations of object analysis.     

In the eye of the beholder: visual experience and categories in the human brain

How does experience change representations of visual objects in the brain? Do cortical object representations reflect category membership? In this issue of Neuron, Jiang et al. show that category training leads to sharpening of neural responses in high-level visual cortex; in contrast, category boundaries may be represented only in prefrontal cortex.     

The effect of emotion and personality on olfactory perception

It is well established that both the emotional tone of sensory stimuli and the personality characteristics of an individual can bias sensory perception. What has largely been unexplored is whether the current emotional state of an individual has a similar effect, and how it works together with other factors. Here we carry out a comprehensive study to examine how olfactory perception is affected by the emotional tone of the stimuli, and the personality and current emotional state of the individual. Subjects reported experiencing happiness, sadness, negativity/hostility and neutrality when exposed to corresponding emotionally themed video clips, and in each case, smelled a suprathreshold pleasant, an unpleasant and a neutral odorant. The time taken for the subject to detect each odorant and the olfactory intensity were recorded. We found that women detected the pleasant odorant faster than the neutral one. In addition, personality modulated reaction time and olfactory intensity, such that neurotic and anxious individuals were selectively biased toward affective rather than neutral odorants. Finally, current emotional state augmented intensity in men but not in women, and differentially influenced the response time. These findings provided new insights into the effects of emotion and personality on olfactory perception.     

The neural basis of visual body perception

The human body, like the human face, is a rich source of socially relevant information about other individuals. Evidence from studies of both humans and non-human primates points to focal regions of the higher-level visual cortex that are specialized for the visual perception of the body. These body-selective regions, which can be dissociated from regions involved in face perception, have been implicated in the perception of the self and the 'body schema', the perception of others' emotions and the understanding of actions.     

Manipulation of pre-target activity on the right frontal eye field enhances conscious visual perception in humans

The right Frontal Eye Field (FEF) is a region of the human brain, which has been consistently involved in visuo-spatial attention and access to consciousness. Nonetheless, the extent of this cortical site's ability to influence specific aspects of visual performance remains debated. We hereby manipulated pre-target activity on the right FEF and explored its influence on the detection and categorization of low-contrast near-threshold visual stimuli. Our data show that pre-target frontal neurostimulation has the potential when used alone to induce enhancements of conscious visual detection. More interestingly, when FEF stimulation was combined with visuo-spatial cues, improvements remained present only for trials in which the cue correctly predicted the location of the subsequent target. Our data provide evidence for the causal role of the right FEF pre-target activity in the modulation of human conscious vision and reveal the dependence of such neurostimulatory effects on the state of activity set up by cue validity in the dorsal attentional orienting network.