Allison B. Sekuler

Aging reduces center-surround antagonism in visual motion processing.

Discriminating the direction of motion of a low-contrast pattern becomes easier with increasing stimulus area. However, increasing the size of a high-contrast pattern makes it more difficult for observers to discriminate motion. This surprising result, termed spatial suppression, is thought to be mediated by a form of center-surround suppression found throughout the visual pathway. Here, we examine the counterintuitive hypothesis that aging alters such center-surround interactions in ways that improve performance in some tasks. We found that older observers required briefer stimulus durations than did younger observers to extract information about stimulus direction in conditions using large, high-contrast patterns. We suggest that this age-related improvement in motion discrimination may be linked to reduced GABAergic functioning in the senescent brain, which reduces center-surround suppression in motion-selective neurons.

Inverting houses and textures : Investigating the characteristics of learned inversion effects

Faces, more than other objects, are identified more accurately when upright than inverted. This inversion effect may be linked to differences in expertise. Here, we explore how stimulus characteristics and expertise interact to determine the magnitude of inversion effects. Observers were trained to identify houses or textures. Inversion effects were not found with either stimulus before training, but were found following 5 days of practice. Additionally, the learning-induced inversion effects showed partial transfer to novel exemplars. Although similar amounts of learning were observed with both types of stimuli, inversion effects were significantly larger for textures. Our results suggest that the size of the inversion effect is not a reliable index of face-specific processing.

Healthy Aging Delays Scalp EEG Sensitivity to Noise in a Face Discrimination Task

We used a single-trial ERP approach to quantify age-related changes in the time-course of noise sensitivity. A total of 62 healthy adults, aged between 19 and 98, performed a non-speeded discrimination task between two faces. Stimulus information was controlled by parametrically manipulating the phase spectrum of these faces. Behavioral 75% correct thresholds increased with age. This result may be explained by lower signal-to-noise ratios in older brains. ERP from each subject were entered into a single-trial general linear regression model to identify variations in neural activity statistically associated with changes in image structure. The fit of the model, indexed by R2, was computed at multiple post-stimulus time points. The time-course of the R2 function showed significantly delayed noise sensitivity in older observers. This age effect is reliable, as demonstrated by test–retest in 24 subjects, and started about 120 ms after stimulus onset. Our analyses suggest also a qualitative change from a young to an older pattern of brain activity at around 47 ± 4 years old.

Visual Memory Decay Is Deterministic

After observers see an object or pattern, their visual memory of what they have seen decays slowly over time. Nearly all current theories of vision assume that decay of short-term memory occurs because visual representations are progressively and randomly corrupted as time passes. We tested this assumption using psychophysical noise-masking methods, and we found that visual memory decays in a completely deterministic fashion. This surprising finding challenges current ideas about visual memory and sets a goal for future memory research: to characterize the deterministic “forgetting function” that describes how memories decay over time.

Spatial characteristics of motion-sensitive mechanisms change with age and stimulus spatial frequency.

Contrast-dependent interactions between classical (CRF) and non-classical regions (nCRF) of visual neuron receptive fields are well documented in primate visual cortex. Physiological models that describe CRF and nCRF interactions in single neurons have recently been applied to psychophysical measures of spatial summation and suppression in motion perception of young adults (Tadin & Lappin, 2005). We wished to determine whether such models could account for the reduction in spatial suppression that occurs in normal aging (Betts et al., 2005). We applied three models to duration thresholds obtained in a simple motion discrimination task using drifting Gabor stimuli that ranged in spatial frequency from 0.5 to 4c/deg. We found that a model in which the center CRF and surrounding nCRF are represented as spatially-overlapping excitatory and inhibitory 2D Gaussians with independent contrast response functions, which we call the Gain model, could account for the effects of aging simply by increasing the spatial extent of the CRF. Two additional models were evaluated. The Size model, which varied the size of the CRF as a function of contrast, produced CRF and nCRF size constants that departed significantly from physiological estimates of receptive field sizes. The Drive model, which yoked the activation of the suppressive nCRF to the CRF response, yielded reasonable fits to the data and suggested an age-related decline in the strength of suppression from the nCRF. However, the Drive model estimated the CRF size parameter to be equal to, or even slightly larger than, the nCRF size parameter, which is inconsistent with the physiological literature. Our findings therefore suggest that the Gain model provides the most plausible estimates of receptive field sizes. Based on this model, age-related increases in the size of central excitatory receptive fields relative to the inhibitory surrounds may contribute to behavioral measures of reduced spatial suppression found in older observers.

How Prevalent Is Object-Based Attention?

Previous research suggests that visual attention can be allocated to locations in space (space-based attention) and to objects (object-based attention). The cueing effects associated with space-based attention tend to be large and are found consistently across experiments. Object-based attention effects, however, are small and found less consistently across experiments. In three experiments we address the possibility that variability in object-based attention effects across studies reflects low incidence of such effects at the level of individual subjects. Experiment 1 measured space-based and object-based cueing effects for horizontal and vertical rectangles in 60 subjects comparing commonly used target detection and discrimination tasks. In Experiment 2 we ran another 120 subjects in a target discrimination task in which rectangle orientation varied between subjects. Using parametric statistical methods, we found object-based effects only for horizontal rectangles. Bootstrapping methods were used to measure effects in individual subjects. Significant space-based cueing effects were found in nearly all subjects in both experiments, across tasks and rectangle orientations. However, only a small number of subjects exhibited significant object-based cueing effects. Experiment 3 measured only object-based attention effects using another common paradigm and again, using bootstrapping, we found only a small number of subjects that exhibited significant object-based cueing effects. Our results show that object-based effects are more prevalent for horizontal rectangles, which is in accordance with the theory that attention may be allocated more easily along the horizontal meridian. The fact that so few individuals exhibit a significant object-based cueing effect presumably is why previous studies of this effect might have yielded inconsistent results. The results from the current study highlight the importance of considering individual subject data in addition to commonly used statistical methods.

9 – Amodal Completion: A Case Study In Grouping

A minimum number of clock pulses required for keeping an electronic component in a waiting condition or state are intermittently applied to the electronic component, thereby minimizing the heat dissipation thereof. A control circuit, utilized in the invention, provides an output signal which permits continuous clock signals to be applied, for example, to memory chips, during read and write periods, but such control circuit reduces the number of clock signals applied to the memory chips during periods when the read and write processes are not required.

Personal familiarity enhances sensitivity to horizontal structure during processing of face identity

What makes identification of familiar faces seemingly effortless? Recent studies using unfamiliar face stimuli suggest that selective processing of information conveyed by horizontally oriented spatial frequency components supports accurate performance in a variety of tasks involving matching of facial identity. Here, we studied upright and inverted face discrimination using stimuli with which observers were either unfamiliar or personally familiar (i.e., friends and colleagues). Our results reveal increased sensitivity to horizontal spatial frequency structure in personally familiar faces, further implicating the selective processing of this information in the face processing expertise exhibited by human observers throughout their daily lives.

Characterizing Population EEG Dynamics throughout Adulthood

Abstract For decades, electroencephalography (EEG) has been a useful tool for investigating the neural mechanisms underlying human psychological processes. However, the amount of time needed to gather EEG data means that most laboratory studies use relatively small sample sizes. Using the Muse, a portable and wireless four-channel EEG headband, we obtained EEG recordings from 6029 subjects 18–88 years in age while they completed a category exemplar task followed by a meditation exercise. Here, we report age-related changes in EEG power at a fine chronological scale for δ, θ, α, and β bands, as well as peak α frequency and α asymmetry measures for both frontal and temporoparietal sites. We found that EEG power changed as a function of age, and that the age-related changes depended on sex and frequency band. We found an overall age-related shift in band power from lower to higher frequencies, especially for females. We also found a gradual, year-by-year slowing of the peak α frequency with increasing age. Finally, our analysis of α asymmetry revealed greater relative right frontal activity. Our results replicate several previous age- and sex-related findings and show how some previously observed changes during childhood extend throughout the lifespan. Unlike previous age-related EEG studies that were limited by sample size and restricted age ranges, our work highlights the advantage of using large, representative samples to address questions about developmental brain changes. We discuss our findings in terms of their relevance to attentional processes and brain-based models of emotional well-being and aging.

Masking of individual facial features reveals the use of horizontal structure in the eyes

3) Pachai et al. (2013). Front Psych, 4. 4) Goffaux & Dakin (2010). Front Psych, 1. 1) Sekuler et al. (2004). Curr Biol, 5. 2) Gold et al. (2012). Psych Sci, 23. This work was supported by NSERC and the Canada Research Chair program. The authors would like to thank Donna Waxman for her assistance and support. Simulated observer  Higher overall masking for the eyes relative to the nose and mouth suggests these features are maximally diagnostic.  Higher masking for horizontal relative to vertical suggests the eyes and mouth contain diagnostic horizontal structure.