Attentional capture by colour and motion in cerebral achromatopsia

Functional neuroanatomy of blindsight revealed by activation likelihood estimation meta-analysis

Blindsight, the residual abilities of patients with cortical blindness to respond proficiently to stimuli they do not consciously acknowledge, offers a unique opportunity to study the functional and anatomical mechanisms sustaining visual awareness. Over decades, the phenomenon has been documented in a wide number of different patients, across independent laboratories, and for a variety of tasks and stimulus properties. Nevertheless, the functional neuroanatomy of blindsight remains elusive and alternative proposals have been put forth. To tackle this issue from a novel perspective, we performed a quantitative Activation Likelihood Estimation (ALE) meta-analysis on the neuroimaging literature available on blindsight. Significant activity was reported in subcortical structures, such as the superior colliculus, pulvinar and amygdala, as well as in cortical extrastriate areas along the dorsal and ventral visual stream. This data-driven functional network collectively defines the extant neural fingerprint of blindsight. To further characterize the unique combination of segregation and integration in brain networks engaged in blindsight, we measured the relationship between active areas and experimental features in the original studies, their clustering and hierarchical organization. Results support a network-based organization in the functional neuroanatomy of blindsight, which likely reflects the intersection of different stimulus properties and behavioural tasks examined. We suggest that the conceptualization of blindsight as a constellation of multiple nonconscious visual abilities is better apt as a summary of present-day wisdom, thereby mirroring the variety of existing V1-independent pathway and their different functional roles.

Real Person Interaction in Visual Attention Research

Abstract. An important development in cognitive psychology in the past decade has been the examination of visual attention during real social interaction. This contrasts traditional laboratory studies of attention, including “social attention,” in which observers perform tasks alone. In this review, we show that although the lone-observer method has been central to attention research, real person interaction paradigms have not only uncovered the processes that occur during “joint attention,” but have also revealed attentional processes previously thought not to occur. Furthermore, the examination of some visual attention processes almost invariably requires the use of real person paradigms. While we do not argue for an increase in “ecological validity” for its own sake, we do suggest that research using real person interaction has greatly benefited the development of visual attention theories.

Do humans spontaneously take the perspective of others?

A growing number of authors have argued that humans automatically compute the visual perspective of other individuals. Evidence for this has come from the dot perspective task in which observers are faster to judge the number of dots in a display when a human avatar has the same perspective as the observer compared to when their perspectives are different. The present experiment examined the 'spontaneous perspective taking' claim using a variant of the dot perspective paradigm in which we manipulated what the avatar could see via physical barriers that either allowed the targets to be seen by the avatar or occluded this view. We found a robust 'perspective taking' effect despite the avatar being unable to see the same stimuli as the participant. These findings do not support the notion that humans spontaneously take the perspective of others.

Fear of holes

Phobias are usually described as irrational and persistent fears of certain objects or situations, and causes of such fears are difficult to identify. We describe an unusual but common phobia (trypophobia), hitherto unreported in the scientific literature, in which sufferers are averse to images of holes. We performed a spectral analysis on a variety of images that induce trypophobia and found that the stimuli had a spectral composition typically associated with uncomfortable visual images, namely, high-contrast energy at midrange spatial frequencies. Critically, we found that a range of potentially dangerous animals also possess this spectral characteristic. We argue that although sufferers are not conscious of the association, the phobia arises in part because the inducing stimuli share basic visual characteristics with dangerous organisms, characteristics that are low level and easily computed, and therefore facilitate a rapid nonconscious response.

A demonstration of direct access to colored stimuli following cueing by color

To test whether cueing by color can affect orienting without first computing the location of the cued color, the impact of reorienting on the validity effect was examined. In Experiment 1 subjects were asked to detect a black dot target presented at random on either of two colored forms. The forms started being presented 750 ms before the onset of a central cue (either an arrow or a colored square). In some proportion of the trials the colors switched locations 150 ms after cue onset, simultaneously with target onset. The color switch was not found to retard responses following a color cue more than following a location cue. Furthermore, it did not reduce the validity effect of the color cue: Though the validity effect of the location cue was quite larger than the validity effect of the color cue, both effects were additive with the presence/absence of a color switch. In Experiment 2, subjects were rather asked to detect a change in shape of one of the colored forms. In this case, color switch was found to affect performance even less following a color cue. The fact that across experiments, color switch did not retard neither responding nor orienting selectively in the color cue condition, indicates that when attention is set to a certain color, reorienting to a new object following color switch does not require re-computing the address of the cued color. That finding is argued to embarrass a strong space-based view of visual attention.

Non-transient luminance changes do not capture attention

The processing of luminance change is a ubiquitous feature of the human visual system and provides the basis for the rapid orienting of attention to potentially important events (e.g., motion onset, object onset). However, despite its importance for attentional capture, it is not known whether a luminance change attracts attention solely because of its status as a sensory transient or can attract attention at a relatively high cognitive level. In a series of six experiments, we presented visual displays in which a single object underwent a luminance change that was either visible or obscured by a mask. A target then appeared either at the change location or elsewhere. The results showed that the luminance change attracted attention only in the visible condition. This was even observed with the largest change we could generate (> 75 cd/m(2)). These data suggest that the importance of a luminance change is only in its status as a low-level sensory transient.

The Prioritization of Feature Singletons in the Change Detection Paradigm

Six experiments are reported investigating whether a discontinuity in colour can accrue attentional priority. In addition to a standard visual search paradigm, we examined the degree to which colour singletons and nonsingletons are susceptible to change blindness. Results showed that changes occurring at colour singletons were relatively more resistant to change blindness. Although suggestive of bottom-up marshalling of attention, no prioritization of the singleton occurred when the most stringent test of stimulus-driven attentional attraction was employed, that is, when attending to the singleton was detrimental to the task. We conclude that a discontinuity in colour will attract attention unless an attentional set is contrary to singletons.

Pupillary responses to coloured and contourless displays in total cerebral achromatopsia

In two patients with total acquired cortical colour blindness and in six control subjects we studied the binocular pupillary response to a variety of sharply defined coloured and grey displays that either had the same mean luminance as the background (isoluminant) or were of greater mean luminance. Despite their complete inability to identify or to discriminate between colours the patients, like the control subjects, showed a pupillary response to the structured coloured displays, even when they were masked by dynamic luminance changes. However, and unlike the control subjects, the patients showed no pupillary response when the coloured displays lacked sharp chromatic borders, as in Gabors or Gaussians. The results indicate that although chromatic processing still occurs in cortical colour blindness its function is solely to give rise to the detection of sharp boundaries which, in their case, can provide the perception of shape but not hue. In accordance with this, the patients could no longer describe the isoluminant borderless figures, which were often totally invisible to them despite their strong chromatic contrast with the background.

Effortless control: executive attention and conscious feeling of mental effort are dissociable

Recruitment of executive attention is normally associated to a subjective feeling of mental effort. Here we investigate the nature of this coupling in a patient with a left mesio-frontal cortex lesion including the anterior cingulate cortex (ACC), and in a group of comparison subjects using a Stroop paradigm. We show that in normal subjects, subjective increases in effort associated with executive control correlate with higher skin-conductance responses (SCRs). However, our patient experienced no conscious feeling of mental effort and showed no SCR, in spite of exhibiting normal executive control, and residual right anterior cingulate activity measured with event-related potentials (ERPs). Finally, this patient demonstrated a pattern of impaired behavior and SCRs in the Iowa gambling task-elaborated by Damasio, Bechara and colleagues-replicating the findings reported by these authors for other patients with mesio-frontal lesions. Taken together, these results call for a theoretical refinement by revealing a decoupling between conscious cognitive control and consciously reportable feelings. Moreover, they reveal a fundamental distinction, observed here within the same patient, between the cognitive operations which are depending on normal somatic marker processing, and those which are withstanding to impairments of this system.