Testing the dorsal stream attention hypothesis: Electrophysiological correlates and the effects of ventral stream damage

The roles of dorsal and ventral processing streams in visual orienting and conscious perception were examined in two experiments. The first employed high density EEG with source localization. The second comprised a neuropsychological case study. Visual orienting was assessed with an attention procedure, where peripheral letters cued participants towards a target location. In the perception procedure participants responded to the same letters by performing an explicit conscious discrimination. In Experiment 1, the peripheral letters elicited rapid dorsal stream activation in the attention procedure, and this activation preceded top-down enhancement of target processing in occipital cortex. In the perception procedure early ventral stream activation was seen. In addition, peripheral letters elicited an “early directing attention negativity” (EDAN) over parietal recording sites in the attention procedure, but not in the perception procedure. In Experiment 2, a patient with a bilateral ventral stream lesion but preserved dorsal stream function showed clear disruption to performance in the perception procedure, whilst exhibiting a normal visual orienting effect in the attention procedure. Taken together these findings (1) highlight the distinct roles of the dorsal and ventral streams in attention and perception, and (2) suggest how these streams might interact, via reentrant effects of attention on perceptual processing.     

Gaze and arrow cueing of attention reveals individual differences along the autism spectrum as a function of target context

Observing averted gaze results in a reflexive shift of attention to the gazed‐at location. In two experiments, participants scoring high and low on the Autism‐Spectrum Quotient questionnaire (AQ; Baron‐Cohen, Wheelwright, Skinner, Martin, & Clubley, 2001 ) observed arrow and gaze cues to investigate cueing effect magnitude as a function of the context in which peripheral targets could appear. While identical cueing effects were found with gaze and arrow cues, the more striking results concerned target stimuli. In Experiment 1, targets could appear on a peripheral face, or on scrambled face parts. Overall, greater cueing effects were found when the target appeared on a face. However, this face bias was only observed in participants with low AQ scores, whereas high AQ scorers oriented more to scrambled features. Experiment 2 found equal cueing to targets appearing on tools, as compared with tool parts. However, individual differences were again observed, where low AQ scorers showed larger cueing towards tools, while high scorers oriented more to scrambled parts, as in Experiment 1. These results support the idea that low AQ individuals orient strongly to objects attended by others. However, since the same results were found for arrow cues, this effect may generalize to all central cues to attention. High AQ scorers possessing many more autistic‐like traits tended to orient more to scrambled shapes, perhaps reflecting a bias for orienting to local details.     

Working memory impairment in people with Williams syndrome: Effects of delay, task and stimuli

Williams syndrome (WS) is a neurodevelopmental disorder associated with impaired visuospatial representations subserved by the dorsal stream and relatively strong object recognition abilities subserved by the ventral stream. There is conflicting evidence on whether this uneven pattern in WS extends to working memory (WM). The present studies provide a new perspective, testing WM for a single stimulus using a delayed recognition paradigm in individuals with WS and typically developing children matched for mental age (MA matches). In three experiments, participants judged whether a second stimulus ‘matched’ an initial sample, either in location or identity. We first examined memory for faces, houses and locations using a 5 s delay (Experiment 1) and a 2 s delay (Experiment 2). We then tested memory for human faces, houses, cat faces, and shoes with a 2 s delay using a new set of stimuli that were better controlled for expression, hairline and orientation (Experiment 3). With the 5 s delay (Experiment 1), the WS group was impaired overall compared to MA matches. While participants with WS tended to perform more poorly than MA matches with the 2 s delay, they also exhibited an uneven profile compared to MA matches. Face recognition was relatively preserved in WS with friendly faces (Experiment 2) but not when the faces had a neutral expression and were less natural looking (Experiment 3). Experiment 3 indicated that memory for object identity was relatively stronger than memory for location in WS. These findings reveal an overall WM impairment in WS that can be overcome under some conditions. Abnormalities in the parietal lobe/dorsal stream in WS may damage not only the representation of spatial location but may also impact WM for visual stimuli more generally.     

Do isoluminant color changes capture attention?

Four experiments are reported in which the effects of peripheral cues on visual orienting were investigated. In the luminance condition, the cues consisted of a peripheral change in stimulus luminance. In the isoluminance condition, the cues consisted of an isoluminant color change, using the transient tritanopic technique. In Experiments 1 and 2, it was found that peripheral luminance cues captured attention, whereas peripheral isoluminance cues did not. In Experiments 3 and 4, the participants detected a peripheral target that was also isoluminant with the background. Under these conditions, it was found that both luminance and isoluminance cues captured attention. The results are discussed in terms of the roles of the dorsal and ventral streams in visual orienting, and it is concluded that our findings provide partial support for the contingent involuntary orienting hypothesis of C. Folk and colleagues.     

Face and location processing in children with early unilateral brain injury

Human visuospatial functions are commonly divided into those dependent on the ventral visual stream (ventral occipitotemporal regions), which allows for processing the ‘what’ of an object, and the dorsal visual stream (dorsal occipitoparietal regions), which allows for processing ‘where’ an object is in space. Information about the development of each of the two streams has been accumulating, but very little is known about the effects of injury, particularly very early injury, on this developmental process. Using a set of computerized dorsal and ventral stream tasks matched for stimuli, required response, and difficulty (for typically-developing individuals), we sought to compare the differential effects of injury to the two systems by examining performance in individuals with perinatal brain injury (PBI), who present with selective deficits in visuospatial processing from a young age. Thirty participants (mean = 15.1 years) with early unilateral brain injury (15 right hemisphere PBI, 15 left hemisphere PBI) and 16 matched controls participated. On our tasks children with PBI performed more poorly than controls (lower accuracy and longer response times), and this was particularly prominent for the ventral stream task. Lateralization of PBI was also a factor, as the dorsal stream task did not seem to be associated with lateralized deficits, with both PBI groups showing only subtle decrements in performance, while the ventral stream task elicited deficits from RPBI children that do not appear to improve with age. Our findings suggest that early injury results in lesion-specific visuospatial deficits that persist into adolescence. Further, as the stimuli used in our ventral stream task were faces, our findings are consistent with what is known about the neural systems for face processing, namely, that they are established relatively early, follow a comparatively rapid developmental trajectory (conferring a vulnerability to early insult), and are biased toward the right hemisphere.     

Eye movements reveal mechanisms underlying attentional biases towards threat

Mechanisms underlying attentional biases towards threat (ABTs), such as attentional avoidance and difficulty of disengagement, are still unclear. To address this issue, we recorded participants' eye movements during a dot detection task in which threatening or neutral stimuli served as peripheral cues. We evaluated response times (RTs) in trials where participants looked at the central fixation cross (not at the cues), as they were required, and number and duration of (unwanted) fixations towards threatening or neutral cues; in all analyses trait anxiety was treated as a covariate. Difficulty in attentional disengagement (longer RTs) was found when peripheral threatening stimuli were presented for 100?ms. Moreover, we observed significantly shorter (unwanted) fixations on threatening than on neutral peripheral stimuli, compatible with an avoidance bias, for longer presentation times. These findings demonstrate that, independent of trait anxiety levels, disengagement bias occurs without eye movements, whereas eye movements are implied in threat avoidance.     

Selective attention and avoidance on a pictorial cueing task during stress in clinically anxious and depressed participants

Although it is well established that attentional biases exist in anxious populations, the specific components of visual orienting towards and away from emotional stimuli are not well delineated. The present study was designed to examine these processes. We used a modified spatial cueing task to assess the speed of engagement and disengagement from supraliminal and masked pictorial cues depicting threat, dysphoria, or neutral content in 36 clinically anxious, 41 depressed and 41 control participants. Participants were randomly assigned to a stress or neutral condition. During stress, anxious participants were slow to disengage from masked left hemifield pictures depicting threat or dysphoria, but were quick to disengage from supraliminal threat pictures. Information processing in anxious participants during stress was characterized by early selective attention of emotional stimuli, occurring prior to full conscious awareness, followed by effortful avoidance of threat. Depressed participants were distinct from the anxious group, displaying selective attention for stimuli depicting dysphoria, but not threat, during the neutral condition. In sum, attentional biases in clinical populations are associated with difficulties in the disengagement component of visual orienting. Further, a vigilant-avoidant pattern of attentional bias may represent a strategic attempt to compensate for the early activation of a fear response.     

Are there unconscious perceptual processes?

Blindsight and vision for action seem to be exemplars of unconscious visual processes. However, researchers have recently argued that blindsight is not really a kind of unconscious vision but is rather severely degraded conscious vision. Morten Overgaard and colleagues have recently developed new methods for measuring the visibility of visual stimuli. Studies using these methods show that reported clarity of visual stimuli correlates with accuracy in both normal individuals and blindsight patients. Vision for action has also come under scrutiny. Recent findings seem to show that information processed by the dorsal stream for online action contributes to visual awareness. Some interpret these results as showing that some dorsal stream processes are conscious visual processes (e.g., Gallese, 2007; Jacob & Jeannerod, 2003). The aim of this paper is to provide new support for the more traditional view that blindsight and vision for action are genuinely unconscious perceptual processes. I argue that individuals with blindsight do not have access to the kind of purely qualitative color and size information which normal individuals do. So, even though people with blindsight have a kind of cognitive consciousness, visual information processing in blindsight patients is not associated with a distinctly visual phenomenology. I argue further that while dorsal stream processing seems to contribute to visual awareness, only information processed by the early dorsal stream (V1, V2, and V3) is broadcast to working memory. Information processed by later parts of the dorsal stream (the parietal lobe) never reaches working memory and hence does not correlate with phenomenal awareness. I conclude that both blindsight and vision for action are genuinely unconscious visual processes.     

Intention formation induces episodic inhibition of distracting stimuli

In two experiments we show that (a) distracting stimuli are inhibited after intention formation, (b) this inhibition is episodic rather than semantic in nature, and (c) inhibition of distracting stimuli is terminated once intentions are completed. In both experiments participants were asked to form an intention to press the space bar in response to six cues (i.e. intention cues). After intention formation we measured accessibility of intention cues, of words that are semantically related to the intention cues (i.e. related cues) and of semantically unrelated words (i.e. control cues). In Experiment 1, we obtained slower responses towards related cues compared with both intention cues and control cues in a recognition task, but not in a lexical decision task. In Experiment 2, we showed that inhibition of related cues is terminated after intention completion. Together these results are consistent with theorizing that inhibition of distracting (i.e. related) stimuli is functional for completing previously formed intentions, and give insight in the nature of inhibitory processes during goal pursuit.     

Is Posner's "beam" the same as Treisman's "glue"?: On the relation between visual orienting and feature integration theory

In the present study we investigated whether the visually allocated "beam" studied by Posner and others is the same visual attentional resource that performs the role of feature integration in Treisman's model. Subjects were cued to attend to a certain spatial location by a visual cue, and performance at expected and unexpected stimulus locations was compared. Subjects searched for a target letter (R) with distractor letters that either could give rise to illusory conjunctions (PQ) or could not (PB). Results from three separate experiments showed that orienting attention in response to central cues (endogenous orienting) showed similar effects for both conjunction and feature search. However, when attention was oriented with peripheral visual cues (exogenous orienting), conjunction search showed larger effects of attention than did feature search. It is suggested that the attentional systems that are oriented in response to central and peripheral cues may not be the same and that only the latter performs a role in feature integration. Possibilities for future research are discussed.     

Disrupted attentional learning in high schizotypy: Evidence of aberrant salience

The relationship between learned variations in attention and schizotypy was examined in two experiments. In Experiment 1, participants low on a negative subscale of schizotypy exhibited an explicit bias in overt attention towards stimuli that were established as predictive of a trial outcome, relative to stimuli that were irrelevant. The same participants also showed a bias in learning about these stimuli when they presented in a novel context. Neither of these effects was observed in participants high in schizotypy. In Experiment 2, participants low on the negative subscale of schizotypy exhibited faster reaction times towards a target that was cued by a stimulus that had a history of predictive validity relative to a stimulus that had a history of irrelevance. Again, this effect was not present in participants high in schizotypy. These results imply a disruption in the normal allocation of attention to cues that have predictive significance in schizotypy.     

The role of spatial attention and other processes on the magnitude and time course of cueing effects

We are quite often exposed to multiple objects present in the visual scene, thus attentional selection is necessary in order to selectively respond to the relevant information. Objects can be selected on the basis of the location they occupy by orienting attention in space. In this paper, we review the evidence showing that attention can be oriented in space either endogenously, on the basis of central cues, predictive of the relevant location, or exogenously, automatically triggered by the salient properties of visual stimuli (peripheral cues). Several dissociations observed between orienting on the basis of the two types of cues have led to the conclusion that they do not represent just two modes of triggering the orienting of the very same attentional mechanism, but rather they modulate processing differently. We present a theoretical framework according to which endogenous predictive cues facilitate target processing by orienting attention, thus amplifying processing at the attended location. In contrast, apart from attentional orienting, peripherally presented discrepant cues might trigger additional cue-target event-integration and event-segregation processes, which modulate processing in a different way, thus leading to cueing effects that are exclusively triggered by peripheral cues.     

Attentional bias in high- and low-anxious individuals: Evidence for threat-induced effects on engagement and disengagement

Attentional bias to threatening visual stimuli (words or pictures) is commonly present in anxious individuals, but not in non-anxious people. There is evidence to show that attentional bias to threat can be induced in all individuals when threat is imposed by threat not of symbolic nature, but by cues that predict aversive stimulation (loud noise or electric shock). However, it is not known whether attentional bias in such situations is still influenced by individual differences in anxiety. This question was addressed in two experiments using a spatial cuing task in which visual cues predicted the occurrence of an aversive event consisting of a loud human scream. Speeded attentional engagement to threat cues was positively correlated with trait anxiety in Experiment 1. Experiment 2 showed that speeded attentional engagement was present only in participants selected for high anxiety but not in low-anxious participants. In both experiments, slower disengagement from threat cues was found in all participants, irrespective of their trait anxiety levels.     

Attentional bias in high- and low-anxious individuals: evidence for threat-induced effects on engagement and disengagement

Attentional bias to threatening visual stimuli (words or pictures) is commonly present in anxious individuals, but not in non-anxious people. There is evidence to show that attentional bias to threat can be induced in all individuals when threat is imposed by threat not of symbolic nature, but by cues that predict aversive stimulation (loud noise or electric shock). However, it is not known whether attentional bias in such situations is still influenced by individual differences in anxiety. This question was addressed in two experiments using a spatial cuing task in which visual cues predicted the occurrence of an aversive event consisting of a loud human scream. Speeded attentional engagement to threat cues was positively correlated with trait anxiety in Experiment 1. Experiment 2 showed that speeded attentional engagement was present only in participants selected for high anxiety but not in low-anxious participants. In both experiments, slower disengagement from threat cues was found in all participants, irrespective of their trait anxiety levels.     

Discrepant visual speech facilitates covert selective listening in "cocktail party" conditions

The presence of congruent visual speech information facilitates the identification of auditory speech, while the addition of incongruent visual speech information often impairs accuracy. This latter arrangement occurs naturally when one is being directly addressed in conversation but listens to a different speaker. Under these conditions, performance may diminish since: (a) one is bereft of the facilitative effects of the corresponding lip motion and (b) one becomes subject to visual distortion by incongruent visual speech; by contrast, speech intelligibility may be improved due to (c) bimodal localization of the central unattended stimulus. Participants were exposed to centrally presented visual and auditory speech while attending to a peripheral speech stream. In some trials, the lip movements of the central visual stimulus matched the unattended speech stream; in others, the lip movements matched the attended peripheral speech. Accuracy for the peripheral stimulus was nearly one standard deviation greater with incongruent visual information, compared to the congruent condition which provided bimodal pattern recognition cues. Likely, the bimodal localization of the central stimulus further differentiated the stimuli and thus facilitated intelligibility. Results are discussed with regard to similar findings in an investigation of the ventriloquist effect, and the relative strength of localization and speech cues in covert listening.     

Landmark use by Clark’s nutcrackers (Nucifraga columbiana): influence of disorientation and cue rotation on distance and direction estimates

Many species have been shown to encode multiple sources of information to orient. To examine what kinds of information animals use to locate a goal we manipulated cue rotation, cue availability, and inertial orientation when the food-storing Clark’s nutcracker (Nucifraga columbiana) was searching for a hidden goal in a circular arena. Three groups of birds were used, each with a different goal–landmark distance. As the distance between the goal and the landmark increased, nutcrackers were less accurate in finding the correct direction to the goal than they were at estimating the distance (Experiment 1). To further examine what cues the birds were using to calculate direction, the featural cues within the environment were rotated by 90° and the birds were either oriented when searching (Experiments 2 and 3) or disoriented (Experiment 3). In Experiment 4, all distinctive visual cues were removed (both internal and external to the environment), a novel point of entry was used and the birds were either oriented or disoriented. We found that disorienting the nutcrackers so that they could not use inertial cues did not influence the birds’ total search error. The birds relied heavily but not completely on cues within the environment, as rotating available cues caused them to systematically shift their search behavior. In addition, the birds also relied to some extent on Earth-based cues. These results show the flexible nature of cue use by the Clark’s nutcracker. Our study shows how multiple sources of spatial information may be important for extracting multiple bearings for navigation.     

Multisensory integration affects visuo-spatial working memory

In the present study, we investigate how spatial attention, driven by unisensory and multisensory cues, can bias the access of information into visuo-spatial working memory (VSWM). In a series of four experiments, we compared the effectiveness of spatially-nonpredictive visual, auditory, or audiovisual cues in capturing participants' spatial attention towards a location where to-be-remembered visual stimuli were or were not presented (cued/uncued trials, respectively). The results suggest that the effect of peripheral visual cues in biasing the access of information into VSWM depend on the size of the attentional focus, while auditory cues did not have direct effects in biasing VSWM. Finally, spatially congruent multisensory cues showed an enlarged attentional effect in VSWM as compared to unimodal visual cues, as a likely consequence of multisensory integration. This latter result sheds new light on the interplay between spatial attention and VSWM, pointing to the special role exerted by multisensory (audiovisual) cues.     

Tiger salamanders’ (<Emphasis Type="Italic">Ambystoma tigrinum</Emphasis>) response learning and usage of visual cues

We explored tiger salamanders’ (Ambystoma tigrinum) learning to execute a response within a maze as proximal visual cue conditions varied. In Experiment 1, salamanders learned to turn consistently in a T-maze for reinforcement before the maze was rotated. All learned the initial task and executed the trained turn during test, suggesting that they learned to demonstrate the reinforced response during training and continued to perform it during test. In a second experiment utilizing a similar procedure, two visual cues were placed consistently at the maze junction. Salamanders were reinforced for turning towards one cue. Cue placement was reversed during test. All learned the initial task, but executed the trained turn rather than turning towards the visual cue during test, evidencing response learning. In Experiment 3, we investigated whether a compound visual cue could control salamanders’ behaviour when it was the only cue predictive of reinforcement in a cross-maze by varying start position and cue placement. All learned to turn in the direction indicated by the compound visual cue, indicating that visual cues can come to control their behaviour. Following training, testing revealed that salamanders attended to stimuli foreground over background features. Overall, these results suggest that salamanders learn to execute responses over learning to use visual cues but can use visual cues if required. Our success with this paradigm offers the potential in future studies to explore salamanders’ cognition further, as well as to shed light on how features of the tiger salamanders’ life history (e.g. hibernation and metamorphosis) impact cognition.     

Integrating faces, houses, motion, and action: spontaneous binding across ventral and dorsal processing streams

Perceiving an event requires the integration of its features across numerous brain maps and modules. Visual object perception is thought to be mediated by a ventral processing stream running from occipital to inferotemporal cortex, whereas most spatial processing and action control is attributed to the dorsal stream connecting occipital, parietal, and frontal cortex. Here we show that integration operates not only on ventral features and objects, such as faces and houses, but also across ventral and dorsal pathways, binding faces and houses to motion and manual action. Furthermore, these bindings seem to persist over time, as they influenced performance on future task-relevant visual stimuli. This is reflected by longer reaction times for repeating one, but alternating other features in a sequence, compared to complete repetition or alternation of features. Our findings are inconsistent with the notion that the dorsal stream is operating exclusively online and has no access to memory.     

Attentional Orienting in Two-dimensional Space

This paper examines how the covert orienting of spatial attention affects motor responses to visual stimuli. Premotor theories, as well as hemi-field inhibition accounts of visual attention predict an increase in response times when a target stimulus appears in the opposite direction to a spatial cue. Some models also suggest that this meridional effect should be increased across oblique meridians. Two types of cue (central and peripheral) were used to orient attention towards locations prior to the onset of visual targets. Simple manual (press button) and saccadic responses were measured. No meridional effects were found with peripheral cues, whereas central cueing produced meridional effects across all meridians. Cueing effects did not vary significantly with two-dimensional axis for either manual or saccadic responses. Increases in response time with cue-target distance were found for both response and cue types. For saccades, distance gradients were shallower moving distally rather than proximally from the cued position. However, simple manual responses did not show this asymmetry. Orienting to central cues also modulated the amplitude of saccades. The results are consistent with an effect of attentional cues in oculomotor centres as well as the existence of actiondependent attentional representations. However, it is proposed that, rather than reflecting oculomotor programming, meridional effects arise from a directional organization within spatio-cognitive representations.