Informational Masking in Aging and Brain-lesioned Individuals.

Auditory stream segregation and informational masking were investigated in brain-lesioned individuals, age-matched controls with no neurological disease, and young college-age students. A psychophysical paradigm known as rhythmic masking release (RMR) was used to examine the ability of participants to identify a change in the rhythmic sequence of 20-ms Gaussian noise bursts presented through headphones and filtered through generalized head-related transfer functions to produce the percept of an externalized auditory image (i.e.

Detection of dynamic changes in interaural delay by older adults (L).

The ability of older adults (48 to 72) with relatively intact low-frequency hearing to detect the motion of an acoustic source was investigated using dynamically varying interaural delays. Thresholds were measured using a single-interval two-alternative forced-choice task in which listeners determined if the sound source was moving or stationary. Motion thresholds were significantly larger than stationary localization thresholds.

The rhythm of attention: Perceptual modulation via rhythmic entrainment is lowpass and attention mediated.

Modulation patterns are known to carry critical predictive cues to signal detection in complex acoustic environments. The current study investigated the persistence of masker modulation effects on postmodulation detection of probe signals. Hickok, Farahbod, and Saberi (Psychological Science, 26, 1006-1013, 2015) demonstrated that thresholds for a tone pulse in stationary noise follow a predictable periodic pattern when preceded by a 3-Hz amplitude modulated masker.

The Rhythm of Perception: Entrainment to Acoustic Rhythms Induces Subsequent Perceptual Oscillation.

Acoustic rhythms are pervasive in speech, music, and environmental sounds. Recent evidence for neural codes representing periodic information suggests that they may be a neural basis for the ability to detect rhythm. Further, rhythmic information has been found to modulate auditory-system excitability, which provides a potential mechanism for parsing the acoustic stream.

Amygdala lateralization at rest and during viewing of neutral faces in major depressive disorder using low-resolution brain electromagnetic tomography.

Neuroimaging experiments of amygdala activity during rest have shown abnormal amygdalar lateralization in Major Depressive Disorder (MDD). The current study is an exploratory investigation of the use of the neuroimaging technique Low Resolution Electromagnetic Tomography (LORETA) to measure current source density (CSD) in the amygdala. We examined seven adults with MDD and nine healthy control subjects at rest, and while they viewed images of emotionally neutral faces.

Chemotopic representations of aromatic odorants in the rat olfactory bulb.

Our laboratory has characterized spatial patterns of evoked neural activity across the entire glomerular layer of the rat olfactory bulb using primarily aliphatic odorants that differ systematically in functional groups and hydrocarbon structures. To represent more fully the true range of odorant chemistry, we investigated aromatic compounds, which have a more rigid molecular structure than most aliphatic compounds and are particularly salient olfactory stimuli for humans. We first investigated glomerular patterns of 2-deoxyglucose uptake in response to aromatic compounds that differ in the nature and position of their functional groups (e.

Effects of functional group position on spatial representations of aliphatic odorants in the rat olfactory bulb.

Principles of olfactory coding can be clarified by studying the olfactory bulb activity patterns that are evoked by odorants differing systematically in chemical structure. In the present study, we used series of aliphatic esters, ketones, and alcohols (27 odorants total) to determine the effects of functional group position on glomerular-layer activity patterns. These patterns were measured as uptake of [(14)C]2-deoxyglucose and were mapped into standardized data matrices for statistical comparison across different rats.

Interactions between odorant functional group and hydrocarbon structure influence activity in glomerular response modules in the rat olfactory bulb.

To investigate the effect of odorant hydrocarbon structure on spatial representations in the olfactory bulb systematically, we exposed rats to odorant chemicals possessing one of four different oxygen-containing functional groups on one of five different hydrocarbon backbones. We also used several hydrocarbon odorants lacking other functional groups. Hydrocarbon structural categories included straight-chained, branched, double-bonded, alicyclic, and aromatic features.

Local and global chemotopic organization: general features of the glomerular representations of aliphatic odorants differing in carbon number.

To determine whether there is a general strategy used by the olfactory system to represent odorants differing in carbon chain length, rats were exposed to homologous series of straight-chained, saturated aliphatic aldehydes, ethyl esters, acetates, ketones, primary alcohols, and secondary alcohols (32 odorants total). Neural activity across the entire glomerular layer of the olfactory bulb was mapped quantitatively by measuring uptake of [14C]2-deoxyglucose evoked by each odorant. Uptake was observed both in dorsal glomerular modules previously associated with the particular odorant functional groups and in more ventral and posterior modules.

Detection of large interaural delays and its implication for models of binaural interaction.

The interaural time difference (ITD) is a major cue to sound localization along the horizontal plane. The maximum natural ITD occurs when a sound source is positioned opposite to one ear. We examined the ability of owls and humans to detect large ITDs in sounds presented through headphones.