Mathematical classification of tight junction protein images.

We present the rationale for the development of mathematical features used for classification of images stained for selected tight junction proteins. The project examined localization of zonula occludens-1, claudin-1 and F-actin in a model epithelium, Madin-Darby canine kidney II cells. Cytochalasin D exposure was used to perturb junctional localization by actin cytoskeleton disruption. Mathematical features were extracted from images to reliably reveal characteristic information of the pattern of protein localization. Features, such as neighbourhood standard deviation, gradient of pixel intensity measurement and conditional probability, provided meaningful information to classify complex image sets. The newly developed mathematical features were used as input to train a neural network that provided a robust method of individual image classification. The ability for researchers to make determinations concerning image classification while minimizing human bias is an important advancement for the field of tight junction cellular biology.

Location and frequency cues in auditory selective attention.

The roles of frequency and location cues in auditory selective attention were investigated in a series of experiments in which target tones were distinguished from distractors by frequency, location, or the conjunction of frequency and location features. When frequency separations in high-rate tone sequences were greater than 1 octave, participants were fastest at identifying targets defined by frequency and were sometimes faster at identifying conjunction than location targets. Frequency salience diminished as filtering demands were reduced: At long interstimulus intervals (> 2.0 s), performance was superior in location conditions. The results suggest that frequency may play a role in auditory selective attention tasks analogous to the role of spatial position in visual attention.

Transient interference of right hemispheric function due to automatic emotional processing.

We examined the effects of emotional stimuli on right and left hemisphere detection performance in a hemifield visual discrimination task. A group of 18 healthy subjects were asked to discriminate between upright and inverted triangles (target). Targets were randomly presented in the left or right visual hemifield (150 ms target duration). A brief emotional picture (pleasant or unpleasant; 150 ms stimulus duration) or neutral picture selected from the International Affective Picture System was randomly presented either in the same (47%) or the opposite (47%) spatial location to the subsequent target. Emotional or neutral stimuli offset 150 ms prior to the subsequent target. Subjects were instructed to ignore the pictures and respond to the targets as quickly and accurately as possible. Independent of field of presentation, emotional stimuli prolonged reaction times (P < 0.01) to LVF targets, with unpleasant stimuli showing a greater effect than pleasant stimuli. The current study shows that brief emotional stimuli selectively impair right hemispheric visual discrimination capacity. The findings suggest automatic processing of emotional stimuli captures right hemispheric processing resources and transiently interferes with other right hemispheric functions.

Conjoining auditory and visual features during high-rate serial presentation: processing and conjoining two features can be faster than processing one.

The time required to conjoin stimulus features in high-rate serial presentation tasks was estimated in auditory and visual modalities. In the visual experiment, targets were defined by color, orientation, or the conjunction of color and orientation features. Responses were fastest in color conditions, intermediate in orientation conditions, and slowest in conjunction conditions. Estimates of feature conjunction time (FCT) were derived on the basis of a model in which features were processed in parallel and then conjoined, permitting FCTs to be estimated from the difference in reaction times between conjunction and the slowest single-feature condition. Visual FCTs averaged 17 msec, but were negative for certain stimuli and subjects. In the auditory experiment, targets were defined by frequency, location, or the conjunction of frequency and location features. Responses were fastest in frequency conditions, but were faster in conjunction than in location conditions, yielding negative FCTs. The results from both experiments suggest that the processing of stimulus features occurs interactively during early stages of feature conjunction.

Aging and the segregation of auditory stimulus sequences.

This study aimed to clarify whether the age-related decline in selective attention widely reported in the literature can be attributed to a selective deficit in the segregation of relevant streams of sound from irrelevant ones. Young and older individuals responded to infrequent deviant stimuli (targets) mixed with distractors in situations that facilitated perception of one or two streams of sounds. Both young and older adults showed the same degree of improvement in performance under conditions that promoted auditory streaming. However, in both listening conditions young subjects were faster and more accurate than older subjects in responding to target zones. Thus, it appears that age-related declines in auditory selective attention cannot be attributed to a selective deficit in the segregation of auditory sequences, but occur in a subsequent stage of processing such as response selection and/or execution.

Brain indices of automatic pattern processing.

The extent to which the auditory system automatically encodes simple auditory patterns was investigated by recording event-related brain potentials (ERPs) to non-attended sounds in subjects reading a book. ERPs were recorded to tones alternating regularly in pitch and to rare breaks in the alternating sequence. In all conditions, breaks in the pattern elicited a right hemisphere dominant fronto-central mismatch negativity (MNN) at a latency of 140-220 ms. The MMN increased in amplitude and decreased in latency with increasing pitch separation and stimulus rate. The results suggest that the processing of auditory patterns occurs automatically and depends on a rapidly fading short-term acoustic memory.