Session Detail

This study examined the time course of voluntarily allocation of attention to a specific point in time. We employed the constant foreperiod and the temporal orienting paradigms. With both paradigms, the task was to identify a letter presented for a brief duration (16 ms), preceded by a warning signal. The warning signal was either auditory or visual, and it was either informative – indicating the most likely foreperiod (the interval between the warning signal and the target), or not. Critically, to avoid effects of exogenous temporal attention both types of warning signal did not include an intensity change. Additionally, unlike previous studies, we included a wide range of foreperiods (25 - 2400 ms). In comparison to a non-informative warning signal, identification accuracy was significantly higher when the warning signal was informative. Importantly, such effects of temporal attention were found with both very long and very short foreperiods, suggesting optimal voluntary allocation of attention within 150 ms and up to 2.5 sec. Given that letter identification was not speeded we can conclude that temporal attention improved perceptual processing, and that endogenous temporal attention is extremely fast – twice as fast as endogenous spatial attention.

 

In visual search, salient objects usually capture attention. However, our previous studies revealed an opposite phenomenon called the collinear masking effect, which is delayed responses to a target overlapping with a salient collinear object. Aging declines the ability of contour integration, which should decrease the collinear masking effect. Nevertheless, aging increases inhibition mechanism of attention which should enlarge the collinear masking effect. The goal of this study is to test whether the collinear masking effect was weaker or stronger with age. Twenty-eight participants, including 12 old adults (74.1 years) and 16 young adults (23.8 years) were recruited. The search display were composed of 9 by 9 white horizontal bars, excepting one column vertical (collinear). The target was a tilted line on one of the bars, which overlapped with the collinear column at chance. The participants discriminated the tilted of the target. The RT differences between overlapping and non-overlapping conditions weighted by average RT is the index of collinear masking effect. The results showed that old adults generated 27.63% of collinear masking effect, which is significantly larger than that of young adults (5.46%).Thus our data support the argument that aging increases inhibition mechanism of attention.

 

The attentional blink (AB) refers to impaired identification of a target when it follows a previous target within 500ms. Some theories posit that the AB disrupts attentional control, namely, the process of matching incoming information to the current attentional set. Others propose that it delays the encoding of fully processed information into working memory, and thus posit that semantic processing is intact during the blink. We show that neither theory provides a complete account of the AB. First, we show that a distractor sharing the target’s defining feature captures attention to the same extent whether it appears within or outside the blink, thereby demonstrating that control over the attentional set is unimpaired by the blink. Second, we show that the AB impairs reports of a target’s color to a lesser extent than reports of its identity, although the target’s defining feature is the same in the two conditions. We conclude that (1) the AB disrupts attentional engagement, a process that enables the rapid extraction of complex visual information and (2) the triggering of an attentional episode and attentional engagement are dissociated during the blink, which demonstrates that these are separate processes.

 

Usually our attention shifts toward the locations previously cued. However, if the cue was presented longer than 300 ms, a reverse effect would be observed, which is called the inhibition of return (IOR). In using gaze direction as a cue, the IOR would be delayed to 2400 ms. Previous studies showed that a more difficult task would delay periphery cued IOR. This study aimed to test whether gaze-induced IOR also altered with task demands. Ninety participants, 30 for each task demand (discrimination, localization, and detection) was recruited. The cue to target onset asynchrony was 1600 ms to 3200 ms. The discrimination task was to determine the triangular direction (upward or downward). The localization task was to determine probe position (left or right to the fixation). The detection task asked participants to determine whether a probe appeared. The results showed that IOR was significant at 2400 ms SOA in all three tasks, and additionally significant at 2800 ms SOA in the discrimination task. Our data show that gaze cues also generate IOR depending on task demands, and delayed IOR when the task was more difficult.

 

Dissimilar images presented at the same retinal locations to the two eyes induce binocular rivalry. Previously, Lunghi et al (JNsci 2014) demonstrated cross-modal effects during binocular rivalry between two stimuli with different flicker rates. Here we aim to investigate the neural correlates of these cross modal effects using frequency-tagging in the EEG. We induced binocular rivalry between two gratings with 4.5Hz- and 20Hz-flicker rates while recording 64-channel EEG. Subjects (N=34) either 1) focused on reporting of binocular rivalry only or 2) reported rivalry as a primary task while performing a secondary cross-modal attention task, in which subjects assessed the congruency between auditory/tactile stimuli with their ongoing rivalry percept. In terms of behavior, we found strong cross-modal effects only when subjects paid attention to the cross-modal stimuli and only for low-frequency stimuli. The strength of the cross-modal effect was positively correlated with performance on the cross-modal attention task. In terms of EEG, we found strong effects of attention to auditory/tactile stimuli over fronto-temporo-parietal electrodes. Our preliminary analysis showed correlation between the EEG response and the behavioral cross-modal effects between occipital and centro-temporal areas. Our paradigm offers a promising avenue to explore the neural correlates of cross-modal perception.

 

Continuous flash suppression (CFS) uses rapidly flickering Mondrian patterns in one eye to suppress a target in the other. CFS is widely used to study unconscious visual processes, yet its temporal tuning is unknown. We used spatio-temporally filtered dynamic noise patterns to produce narrow-band maskers and probed the temporal, spatial and orientation tuning of CFS. Surprisingly, CFS suppression peaks very prominently at ~1 Hz, well below typical CFS flicker rates of 10 Hz, and is greater for high spatial frequencies. Orientation filtering revealed CFS suppression is strongly orientation tuned at low temporal frequencies, but much less so at high frequencies. CFS suppression also increased with masker contrast and size. The observed selectivity for low temporal and high spatial frequencies, and a rising monotonic contrast function, suggest parvocellular/ventral mechanisms underlie CFS suppression, similar to the binocular rivalry, and thus unifies the two phenomenon previously thought to require different explanations. A better understanding of the tuning parameters of CFS suppression will help optimise this popular technique for removing target images from conscious awareness.

 

Many types of learning take hold gradually and require practice. Yet, when we replay and strengthen memories, we may not realize we are practicing. Memory reactivation during sleep may contribute to the consolidation of memories that produces enduring long-term storage. This reactivation can be investigated via a procedure known as Targeted Memory Reactivation (TMR), in which sensory stimulation is used to modify neural activity while avoiding arousal from sleep. We have found that sounds heard in association with visuospatial learning can be presented again during slow-wave sleep to promote the reactivation of memories. Post-sleep memory testing showed that memory could be systematically and selectively improved. Similar results were obtained with several other types of memory. In some of these experiments, measures of sleep physiology were associated with memory improvement. Brain rhythms can also be entrained during sleep to help understand relevant neurophysiological mechanisms. This research is thus beginning to elucidate critical contributions of sleep to memory consolidation. Furthermore, these methods offer new opportunities for reinforcing learning to enhance clinical outcomes in conjunction with therapies engaged during waking.