Occipital Activation by Pattern Recognition in the Early Blind Using Auditory Substitution for Vision

Early onset blindness leads to a dramatic alteration in the way the world is perceived, a change that is detectable in the organization of the brain. Several studies have confirmed that blindness leads to functional alterations in occipital cortices that normally serve visual functions. These reorganized brain regions respond to a variety of tasks and stimuli, but their specific functions are unclear. In sighted individuals, several studies have reported preparatory activity in retinotopic areas, which enhances perceptual sensitivity. "Baseline shifts," changes in activity associated with a cue predicting an upcoming event, provides a marker for attentional modulation. Here we demonstrate that, in early blind subjects, medial occipital areas produced significant blood oxygenation level-dependent (BOLD) responses to a cue signaling an auditory discrimination trial but not to a cue indicating a no-trial period. Furthermore, the amplitude of the BOLD response in the anterior calcarine sulcus of early blind subjects correlated with their discrimination performance on the auditory backward masking task. Preparatory BOLD responses also were present in auditory cortices, although they were more robust in blind than sighted control subjects. The pattern of response in visual areas is similar to preparatory effects observed during visual selective attention in sighted subjects and consistent with the hypothesis that the mechanisms implicated in visual attention continue to modulate occipital cortex in the early blind. A possible source of this top-down modulation may be the frontoparietal circuits that retain their connectivity with the reorganized occipital cortex and as a result influence processing of nonvisual stimuli in the blind.

Using probabilistic diffusion tractography, we examined the retinotopic organization of splenial callosal connections within early blind, anophthalmic, and control subjects. Early blind subjects experienced prenatal retinal “waves” of spontaneous activity similar to those of sighted subjects, and only lack postnatal visual experience. In anophthalmia, the eye is either absent or arrested at an early prenatal stage, depriving these subjects of both pre- and postnatal visual input. Therefore, comparing these two groups provides a way of separating the influence of pre- and postnatal retinal input on the organization of visual connections across hemispheres. We found that retinotopic mapping within the splenium was not measurably disrupted in early blind or anophthalmic subjects compared to visually normal controls. No significant differences in splenial volume were observed across groups. No significant differences in diffusivity were found between early blind subjects and sighted controls, though some differences in diffusivity were noted between anophthalmic subjects and controls. These results suggest that neither prenatal retinal activity nor postnatal visual experience plays a role in the large-scale topographic organization of visual callosal connections within the splenium.

Objective. To date, most research on electroencephalography (EEG)-based mental workload detection for passive brain-computer interface (pBCI) applications has focused on identifying the overall level of cognitive resources required, such as whether the workload is high or low. We propose, however, that being able to determine the specific type of cognitive resources being used, such as visual or auditory, would also be useful. This would enable the pBCI to take more appropriate action to reduce the overall level of cognitive demand on the user. For example, if a high level of workload was detected and it is determined that the user is primarily engaged in visual information processing, then the pBCI could cause some information to be presented aurally instead. In our previous work we showed that EEG could be used to differentiate visual from auditory processing tasks when the level of processing is high, but the two modalities could not be distinguished when the level of cognitive processing demand was very low. The current study aims to build on this work and move toward the overall objective of developing a pBCI that is capable of predicting both the level and the type of cognitive resources being used. Approach. Fifteen individuals undertook carefully designed visual and auditory tasks while their EEG data was being recorded. In this study, we incorporated a more diverse range of sensory processing conditions including not only single-modality conditions (i.e. those requiring one of either visual or auditory processing) as in our previous study, but also dual-modality conditions (i.e. those requiring both visual and auditory processing) and no-task/baseline conditions (i.e. when the individual is not engaged in either visual or auditory processing). Main results. Using regularized linear discriminant analysis within a hierarchical classification algorithm, the overall cognitive demand was predicted with an accuracy of more than 86%, while the presence or absence of visual and auditory sensory processing were each predicted with an accuracy of approximately 70%. Significance. The findings support the feasibility of establishing a pBCI that can determine both the level and type of attentional resources required by the user at any given moment. This pBCI could assist in enhancing safety in hazardous jobs by triggering the most effective and efficient adaptation strategies when high workload conditions are detected.

The effect of blindness on sound source identification was studied. Four groups of normally-hearing adults, two sighted and two blind, participated. Subjects were tested using arrays of four and eight loudspeakers, surrounding them in the horizontal plane. One sighted group was tested in quiet. The other groups were tested in continuous 60-dB SPL white noise. Three 75-dB SPL 300-ms stimuli were localized: one-third octave noise bands, centered at 0.5 and 4 kHz, and broadband noise. Broadband noise was easiest to localize (both binaural and spectral cues available), and the 0.5-kHz noise band was the most difficult (primarily interaural temporal difference cue available). Subjects with late-onset blindness achieved significantly higher scores than the early blind and blindfolded sighted subjects. The percentage correct decreased with an increase in the number of speakers, but background noise had no effect. The results attest to the benefit of early visual experience for spatial hearing in adulthood, and demonstrate the negative impact of sudden loss of sight.

There is a large amount of variability in performance in masked-speech reception tasks, as well as in psychophysical auditory temporal processing tasks, between listeners with normal or relatively normal low-frequency hearing. In this study we used a cross-sectional dataset collected on 102 listeners (34 young, 34 middle-aged, 34 older) to assess whether variance in these tasks could be explained by variance in subcortical electrophysiological measures of auditory function (auditory brainstem responses and frequency following responses), and whether variance in speech-reception performance could be explained by variance in auditory temporal processing tasks. The potential confounding effect of high-frequency sensitivity was strictly controlled for by using highpass masking noise. Because each high-level construct (masked-speech reception, auditory temporal processing, and subcortical electrophysiological function) was indexed by several variables, we used principal component analyses to reduce the dimensionality of the dataset. Multiple-regression models were then used to assess the associations between the extracted principal components while controlling for a range of possible confounders including age and audiometric thresholds. We found that masked-speech reception was credibly associated with psychophysical auditory temporal processing abilities. No credible associations were found between masked-speech reception and electrophysiological measures of subcortical auditory function, or between psychophysical measures of auditory temporal processing and electrophysiological measures of subcortical auditory function. These results suggest that either the electrophysiological measures of subcortical auditory function used were not sufficiently sensitive to the subcortical neural processes limiting performance in the speech-reception and psychophysical auditory temporal-processing tasks, or that variance in these tasks is largely unrelated to variance in subcortical neural processes in listeners with near-normal hearing.

The haptic horizontal-vertical illusion was studied in two experiments. In Experiment 1, the illusion was relatively weak in sighted subjects and depended on stimulus size and the nature of the figure, that is, whether the pattern was an inverted-T or L shape. Experiment 2 compared early blind and late blind subjects. The illusion was present for an inverted-T figure but absent for an L figure in late blind subjects. However, the early blind subjects treated both the L and T figures as similar and showed the illusion to both. These results support the idea that visual experience may alter haptic judgments in sighted and late blind subjects.

Early blind people compensate for their lack of vision by developing superior abilities in the remaining senses such as audition (Collignon et al., 2006; Gougoux et al., 2004; Wan et al., 2010). Previous studies reported supra-normal abilities in auditory spatial attention, particularly for the localization of peripheral stimuli in comparison with frontal stimuli (Lessard et al., 1998; Röder et al., 1999). However, it is unknown whether this specific supra-normal ability extends to the non-spatial attention domain. Here we compared the performance of early blind subjects and sighted controls, who were blindfolded, during an auditory non-spatial attention task: target detection among distractors according to tone frequency. We paid a special attention to the potential effect of the sound source location, comparing the accuracy and speed in target detection in the peripheral and frontal space. Blind subjects displayed shorter reaction times than sighted controls for both peripheral and frontal stimuli. Moreover, in the two groups of subjects, we observed an interaction effect between the target location and the distractors location: the target was detected faster when its location was different from the location of the distractors. However, this effect was attenuated in early blind subjects and even cancelled in the condition with frontal targets and peripheral distractors. We conclude that early blind people compensate for the lack of vision by enhancing their ability to process auditory information but also by changing the spatial distribution of their auditory attention resources.

Auditory identification of frequency-modulated sweeps and reading difficulties in Chinese

The ability of blind and blindfolded sighted subjects to discriminate cubes of different heights was measured using the method of constant stimuli. Five male blind and 5 male blindfolded sighted students, ages 22 to 28 years, were subjects. All blind subjects had undergone orientation and mobility training at a school for the blind. The cubes, made of wood, were explored using a long cane. Subjects were presented the standard cube and a comparison cube and required to judge whether the comparison cube height was taller, the same, or shorter than the standard. Analysis showed that the difference thresholds of blind and blindfolded sighted subjects were 1.93 and 2.14 cm, respectively. No significant difference in accuracy of discrimination was found between the two groups. The blind subjects showed significantly better performance than the blindfolded sighted subjects on the discrimination task. The blind subjects performed the task significantly faster than the blindfolded sighted subjects. The results suggest that braille reading, use of a long cane, and daily physical activities which required prolonged haptic or proprioceptive learning, may enhance nonvisual motor skills.

Individual differences in the ability to focus and divide attention

When and where are decisions made? In the visual system a saccade, which is a fast shift of gaze toward a target in the visual scene, is the behavioral outcome of a decision. Current neurophysiological data and reaction time models show that saccadic reaction times are determined by a build-up of activity in motor-related structures, such as the frontal eye fields. These structures depend on the sensory evidence of the stimulus. Here we use a delayed figure-ground detection task to show that late modulated activity in the visual cortex (V1) predicts saccadic reaction time. This predictive activity is part of the process of figure-ground segregation and is specific for the saccade target location. These observations indicate that sensory signals are directly involved in the decision of when and where to look.

Neural correlates of olfactory processing in congenital blindness

Objects or events in the universe are perceived by biological systems as patterns. Pattern recognition is a process which assigns these sensory stimuli into perceptually meaningful categories. For the last four decades a considerable effort has been made to simulate the human pattern recognition capabilities by a machine. This quest for automation of pattern recognition processes is primarily driven by applications in computer vision for flexible manufacturing, speech recognition, text recognition, remote sensing, medicine and others. In computer vision for robots, for instance, the pattern recognition task may involve identification of object shape. In speech recognition the object categories may be words, phonemes or diphones and the sensory data on which classification is based could be vector quantised speech signal. In text recognition the objects of interest are characters and their groups forming words. Object categories in remote sensing relate to land cover and the sensory data are reflected energies in several spectral channels of the electromagnetic spectrum.

This study investigated the effect of variable interstimulus intervals (ISIs) on behavioral reaction time (RT) and on the latency and amplitude of the auditory P300 using an auditory continuous performance task (ACPT) paradigm. Twenty subjects were instructed to respond to common stimuli and ignore a rare stimulus. Common stimuli were 1000-, 1500-, and 2000-Hz pure tones. The rare stimulus was a 250-Hz pure tone. ISIs of 1, 2, and 4 seconds were used for this investigation. A significant correlation between ISI, reaction time, P300 latency, correct rejections, and false alarm rates was found. A significant correlation between P300 latency, P300 amplitude, correct rejections, and false alarm rates was also observed. Likewise, a statistically significant increase in reaction time (RT) was observed as ISI increased. The ACPT paradigm in conjunction with the auditory P300 response can measure both behavioral and electrophysiologic changes that occur during active auditory attention and auditory cognitive processing tasks.

Finding a vast array of applications, the problem of computing the convex hull of a set of sorted points in the plane is one of the fundamental tasks in pattern recognition, morphology and image processing. The main contribution of this paper is to show a simple parallel algorithm for computing the convex hull of a set of n sorted points in the plane and evaluate the performance on the dual quad-core processors. The experimental results show that, our implementation achieves a speed-up factor of approximately 7 using 8 processors. Since the speed-up factor of more than 8 is not possible, our parallel implementation for computing the convex hull is close to optimal. Also, for 2 or 4 processors, we achieved a super linear speed up.