Neural Mechanisms of Selective Auditory Attention in Rats (Dissertation)

How does attention modulate sensory representations? In order to probe the underlying neural mechanisms, we established a simple rodent model of modality-specific attention. Rats were trained to perform distinct auditory two-tone discrimination and olfactory odor discrimination in a two alternative choice (2AC) paradigm. 
To determine auditory cortex’s role in this frequency discrimination task, we used GABA-A receptor agonist muscimol to transiently and reversibly inactivate auditory cortexes bilaterally in rats performing simple interleaved auditory and olfactory discrimination. With olfactory discrimination performance serving as internal control for motivation and decision making capability, we found only auditory two-tone discrimination was selectively impaired in these rats. This shows the auditory cortex is involved in this two-tone discrimination task.
To investigate the neural correlate of modality-specific attention in the auditory cortex, we trained rats to perform interleaved auditory and olfactory blocks (of 50~70 trials each) in a single session. In auditory blocks, pure tones were either presented with or without a neutral odor (caproic acid, n=2 and 3 respectively), and subjects were rewarded for discriminating auditory stimuli. In olfactory blocks, both task odors and pure tones were presented simultaneously, and subjects were rewarded for discriminating olfactory stimuli. We recorded neural responses in primary auditory cortex (area A1) in freely moving rats while subjects performed this behavior. Single unit responses to tones were heterogeneous, and included transient, sustained, and suppressed. We found 205 of 802 units recorded responsive to the stimuli we used. Of these 205 units, 18.5% showed modality-specific attentional modulation of the anticipatory activity before tone onset. In addition, we also observed in smaller proportion of units (11.2%) modality-specific attentional modulation of the tone-evoked responses; in most cases, the responses to a particular auditory stimulus was enhanced in the auditory block (or, equivalently, suppressed in the olfactory block). Attention increased choice probability of the population in the auditory block. We have also observed significant behavior choice probability in small proportions of units. 
Our results suggest that shifting attention between audition to olfaction tasks can modulate the activity of single neurons in primary auditory cortex

Identifying Protective Factors in Response to Discriminatory Experiences among Pregnant African American Woman

Adverse maternal-fetal health outcomes, such as low birth weight and preterm delivery, are disproportionately more likely among African-Americans than Non-Hispanic Whites. Experiences of discrimination have been hypothesized as a contributing factor to the large discrepancies in maternal-fetal health outcomes. It is well understood that with increased levels of self-reported discrimination, there are lower ratings of physical and mental health, and higher reporting rates of depressive symptoms; this relationship is stronger in women. In addition to this, skin tone has long been a marker for social class and opportunity, but research on skin tone as a risk factor for African Americans has been less extensive. How skin tone modulates the experience of discrimination for African American women and subsequent maternal-fetal health outcomes still remains a topic of interest. Variations in skin complexion have been implicated in affecting protective factors such as self-esteem and mastery. We aim to identify themes in an interview survey that explores the relationship between self-perceived complexion and the aforementioned protective factors that African American women possess in response to discriminatory experiences. In this project, we propose to complete an exploratory interview among pregnant African American women concerning protective factors in response to discriminatory experiences. Factors to be addressed include reflections on previously encountered discriminatory experiences, self-perceived complexion, mastery, and self-esteem

Colorism: A Darker Shade of Pale

In this article, Professor Banks argues that colorism, skin tone discrimination against dark-skinned but not light-skinned blacks, constitutes a form of race-based discrimination. Skin tone discrimination coexists with more traditional forms of race discrimination that impact all blacks without regard to skin tone and phenotype, yet courts seem unwilling to recognize this point. Professor Banks uses employment discrimination cases to illustrate some courts\u27 willingness to acknowledge subtler forms of race-based discrimination, like skin tone discrimination, for white ethnic and Latina/o plaintiffs, but not for black plaintiffs. The inability of courts to fashion coherent approaches to colorism claims involving black claimants means that dark-skinned blacks will continue to experience more extreme forms of race discrimination than experienced by light-skinner blacks. In addition, failure to address colorism by black litigants will have broader implications as courts face the more complex race-like cases likely [to] occur in the twenty-first century

The Effects of Skin Tone on the Perception of Discrimination in Young African American Women

This research focuses on the perceived discriminatory experiences (i.e. colorism and racism) that young African American women report as a function of their actual and perceived skin tone. Colorism is a form of internalized racism when individuals with darker skin tones are discriminated against by others. Each participant (N = 76) was given the Pantone Skin Tone guide and asked to find the best color (varying on undertone and lightness) that matched closely to their skin tone without feedback from any reflective surfaces and with a handheld mirror. Following that, the researcher identified the participant’s skin tone. In addition, participants completed several research questionnaires assessing perceived racism and discrimination. Participants did report discrimination and biases that they regularly experience based on their skin tone and race. Interestingly, there was no relationship between skin tone and reported discrimination. While qualitative data suggests that colorism does exist, the quantitative data did not establish a link between lightness of one’s skin tone and levels of perceived discrimination. However, individuals who reported a high frequency of experiencing racism in their lives also perceived their skin tone darker without the mirror than with it. This finding establishes a link between negative race-based experiences and one’s self-perception of skin tone. While self-esteem did not moderate or mediate the skin tone-discrimination relationship, it was strongly related to reports of racism and colorism

Skin Tone's Decreasing Importance on Employment: Evidence from a Longitudinal Dataset, 1985-2000

We investigate the effect of skin tone on employment probabilities in a longitudinal data set. Using an objective measure of skin tone from a light-spectrometer and a self-reported measure of race we find that over time the effect of skin tone on employment has diminished. These results hold both across the white and African-American samples as well as within the African-American sample itself with regard to skin tone. Further investigation indicates that all of the gains can be attributed to African-American women; there are no changes in the employment probabilities for African-American men in the 15 year panel data. We find that the expansion of employment for women is concentrated in the services occupations.race, gender, employment discrimination, skin tone, panel data

Reduction of internal noise in auditory perceptual learning

This paper examines what mechanisms underlie auditory perceptual learning. Fifteen normal hearing adults performed two-alternative, forced choice, pure tone frequency discrimination for four sessions. External variability was introduced by adding a zero-mean Gaussian random variable to the frequency of each tone. Measures of internal noise, encoding efficiency, bias, and inattentiveness were derived using four methods (model fit, classification boundary, psychometric function, and double-pass consistency). The four methods gave convergent estimates of internal noise, which was found to decrease from 4.52 to 2.93 Hz with practice. No group-mean changes in encoding efficiency, bias, or inattentiveness were observed. It is concluded that learned improvements in frequency discrimination primarily reflect a reduction in internal noise. Data from highly experienced listeners and neural networks performing the same task are also reported. These results also indicated that auditory learning represents internal noise reduction, potentially through the re-weighting of frequency-specific channels

Perception of nonnative tonal contrasts by Mandarin-English and English-Mandarin sequential bilinguals

This study examined the role of acquisition order and crosslinguistic similarity in influencing transfer at the initial stage of perceptually acquiring a tonal third language (L3). Perception of tones in Yoruba and Thai was tested in adult sequential bilinguals representing three different first (L1) and second language (L2) backgrounds: L1 Mandarin-L2 English (MEBs), L1 English-L2 Mandarin (EMBs), and L1 English-L2 intonational/non-tonal (EIBs). MEBs outperformed EMBs and EIBs in discriminating L3 tonal contrasts in both languages, while EMBs showed a small advantage over EIBs on Yoruba. All groups showed better overall discrimination in Thai than Yoruba, but group differences were more robust in Yoruba. MEBs’ and EMBs’ poor discrimination of certain L3 contrasts was further reflected in the L3 tones being perceived as similar to the same Mandarin tone; however, EIBs, with no knowledge of Mandarin, showed many of the same similarity judgments. These findings thus suggest that L1 tonal experience has a particularly facilitative effect in L3 tone perception, but there is also a facilitative effect of L2 tonal experience. Further, crosslinguistic perceptual similarity between L1/L2 and L3 tones, as well as acoustic similarity between different L3 tones, play a significant role at this early stage of L3 tone acquisition.Published versio

The effect of stimulus range on two-interval frequency discrimination

It has traditionally been thought that performance in two-interval frequency discrimination tasks decreases as the range over which the standard tone varies is increased. Recent empirical evidence and a reexamination of previous results suggest that this may not be the case. The present experiment found that performance was significantly better when the standard roved over a wide range (1500 Hz) than a narrow range (30 Hz). This pattern cannot readily be accommodated by traditional models of frequency discrimination based on memory or attention, but may be explicable in terms of neural plasticity and the formation of perceptual anchors

The perception of lexical tone contrasts in Cantonese children with and without Specific Language Impairment (SLI)

Purpose: This study examined the perception of fundamental frequency (f0) patterns by Cantonese children with and without specific language impairment (SLI). Method: Participants were 14 five-year-old children with SLI, and 14 age-matched (AM) and 13 four-year-old vocabulary-matched (VM) controls. The children identified a word from familiar word pairs that illustrated the 8 minimally contrastive pairs of the 6 lexical tones. They discriminated the f0 patterns within contrastive tonal pairs in speech and nonspeech stimuli. Results: In tone identification, the SLI group performed worse than the AM group but not the VM group. In tone discrimination, the SLI group did worse than the AM group on 2 contrasts and showed a nonsignificant trend of poorer performance on all contrasts combined. The VM group generally did worse than the AM group. There were no group differences in discrimination performance between speech and nonspeech stimuli. No correlation was found between identification and discrimination performance. Only the normal controls showed a moderate correlation between vocabulary scores and performance in the 2 perception tasks. Conclusion: The SLI group's poor tone identification cannot be accounted for by vocabulary knowledge alone. The group's tone discrimination performance suggests that some children with SLI have a deficit in f0 processing. © American Speech-Language-Hearing Association.postprin