Interpreting the orientation of objects: A cross-disciplinary review.

Is object orientation an inherent aspect of the shape of the object or is it represented separately and bound to the object shape in a similar way to other features, such as colour? This review brings together findings from neuropsychological studies of patients with agnosia for object orientation and experimental studies of object perception in healthy individuals that provide converging evidence of separate processing of object identity and orientation. Individuals with agnosia for object orientation, which typically results from damage to the right parietal lobe, can recognize objects presented in a range of orientations yet are unable to interpret or discriminate the objects' orientation. Healthy individuals tested with briefly presented objects demonstrate a similar dissociation: object identity is extracted rapidly in an orientation-invariant way, whereas processing the object's orientation is slower, requires attention and is influenced by the degree of departure from the canonical orientation. This asymmetry in processing can sometimes lead to incorrect bindings between the identity and orientation of objects presented in close temporal proximity. Overall, the available evidence indicates that object recognition is achieved in a largely orientation-invariant manner and that interpreting the object's orientation requires an additional step of mapping this orientation-invariant representation to a spatial reference frame.

Retrieval-induced forgetting with novel visual stimuli is retrieval-specific and strength- independent.

Retrieval-induced forgetting (RIF) is the phenomenon whereby remembering a subset of learned items can reduce memory for other related items. There are two main explanations for this effect: the competition account and the inhibition account. Most research to date has favoured the inhibition account, though two potential confounds have been identified in the evidence for key predictions of the account: (1) Using binary measures of accuracy may make it difficult to detect correlations between the magnitude of RIF and the increase in recall for practised items that is predicted by the competition account (strength dependence), and (2) typical non-competitive restudy may be too weak a form of practice to elicit detectible RIF effects. The present study aimed to test these contentions by adapting the RIF paradigm to allow a more graded measurement of memory strength and a more active form of non-competitive practice. We trained participants (N = 87) to draw sets of novel shapes from memory, using colour as a category cue and overlaid patterns as individual item recall cues. Responses were graded based on the number of features present and items underwent retrieval practice, copying practice (as a more effective form of restudy), or no practice. The results demonstrated RIF in the retrieval practice condition, but no evidence of RIF in the restudy condition, despite a large memory gain for practised items, supporting the notion of retrieval specificity. There was no evidence of strength dependence in any condition. Our results are consistent with the forgetting in this experiment being driven by inhibition.

Sharing the load: How a personally coloured calculator for grapheme-colour synaesthetes can reduce processing costs.

Synaesthesia refers to a diverse group of perceptions. These unusual perceptions are defined by the experience of concurrents; these are conscious experiences that are catalysed by attention to some normally unrelated stimulus, the inducer. In grapheme-colour synaesthesia numbers, letters, and words can all cause colour concurrents, and these are independent of the actual colour with which the graphemes are displayed. For example, when seeing the numeral '3' a person with synaesthesia might experience green as the concurrent irrespective of whether the numeral is printed in blue, black, or red. As a trait, synaesthesia has the potential to cause both positive and negative effects. However, regardless of the end effect, synaesthesia incurs an initial cost when compared with its equivalent example from normal perception; this is the additional processing cost needed to generate the information on the concurrent. We contend that this cost can be reduced by mirroring the concurrent in the environment. We designed the Digital-Colour Calculator (DCC) app, allowing each user to personalise and select the colours with which it displays its digits; it is the first reported example of a device/approach that leverages the concurrent. In this article we report on the reactions to the DCC for a sample of fifty-three synaesthetes and thirty-five non-synaesthetes. The synaesthetes showed a strong preference for the DCC over its normal counterpart. The non-synaesthetes showed no obvious preference. When using the DCC a subsample of the synaesthete group showed consistent improvement in task speed (around 8%) whereas no synaesthete showed a decrement in their speed.

Working memory load reduces corticospinal suppression to former go and trained no-go cues.

Environmental cues associated with an action can prime the motor system, decreasing response times and activating motor regions of the brain. However, when task goals change, the same responses to former go-associated cues are no longer required and motor priming needs to be inhibited to avoid unwanted behavioural errors. The present study tested whether the inhibition of motor system activity to presentations of former go cues is reliant on top-down, goal-directed cognitive control processes using a working memory (WM) load manipulation. Applying transcranial magnetic stimulation over the primary motor cortex to measure motor system activity during a Go/No-go task, we found that under low WM, corticospinal excitability was suppressed to former go and trained no-go cues relative to control cues. Under high WM, the cortical suppression to former go cues was reduced, suggesting that the underlying mechanism required executive control. Unexpectedly, we found a similar result for trained no-go cues and showed in a second experiment that the corticospinal suppression and WM effects were unrelated to local inhibitory function as indexed by short-interval intracortical inhibition. Our findings reveal that the interaction between former response cues and WM is complex and we discuss possible explanations of our findings in relation to models of response inhibition.

Working Memory in Pediatric Epilepsy: A Systematic Review and Meta-Analysis.

Working memory is a multicomponent system that is supported by overlapping specialized networks in the brain. Baddeley's working memory model includes four components: the phonological loop, visuo-spatial sketchpad, the central executive, and episodic buffer. The aim of this review was to establish the gravity and pattern of working memory deficits in pediatric epilepsy. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement guided electronic searches. Sixty-five studies were included in the review. Meta-analyses revealed significant impairments across each working memory component: phonological loop (g = 0.739), visuo-spatial sketchpad (g = 0.521), and central executive (g = 0.560) in children with epilepsy compared to controls. The episodic buffer was not examined. The pattern of impairments, however, differed according to the site and side of seizure focus. This suggests that working memory components are differentially vulnerable to the location of seizure focus in the developing brain.

Repetition blindness for words and pictures: A failure to form stable type representations?

Repetition blindness (RB) is the failure to detect and report a repeated item during rapid serial visual presentation (RSVP). The RB literature reveals consistent and robust RB for word stimuli, but somewhat variable RB effects for pictorial stimuli. We directly compared RB for object pictures and their word labels, using exactly the same procedure in the same participants. Experiment 1 used a large pool of stimuli that only occurred once during the experiment and found significant RB for words, but significant repetition facilitation for pictures. These differential repetition effects were replicated when the task required participants to only report the last item of the stream. Experiment 2 used a small pool of stimuli presented several times throughout the experiment. Significant RB was found for both words and pictures, although it was more pronounced for words. These findings present a challenge to the token individuation hypothesis (Kanwisher, Cognition, 27, 117-143, 1987) and suggest that RB is more likely to be due to a difficulty in establishing a robust type representation. We propose that an experimental context that contains high levels of overlap in visual features (e.g., letters in the case of words, visual fragments in the case of repeatedly presented pictures) may prevent the formation of distinct object-level episodic representations, resulting in RB.

Binding identity and orientation in object recognition.

We tested whether an object's orientation is inherently bound to its identity in a holistic view-based representation at the early stages of visual identification, or whether identity and orientation are represented separately. Observers saw brief and masked stimulus sequences containing two rotated objects. They had to detect if a previously cued object was present in the sequence and report its orientation. In Experiments 1 and 2, the objects were presented sequentially in the same spatial location for 70 ms each, whereas in Experiments 3 and 4 they were presented simultaneously in different spatial locations for 70 ms and 140 ms, respectively. Across all experiments, observers reported the correct orientation for approximately 70% of the positively identified objects, and were at chance in reporting the orientation when they had not recognized the object. This finding suggests that orientation information is accessed after an object has been identified. In addition, when the two objects were presented sequentially in the same spatial location, orientation errors were not random-observers tended to report the orientation of the alternative object in the sequence, indicating misbindings between the identities and orientations of objects that share spatial location. This susceptibility to binding errors was not observed when the objects were in different spatial locations. These results suggest that identity and orientation may be prone to misbinding, and that spatial location may serve to protect their joint integrity.

Substantiating synesthesia: a novel aid in a case of grapheme-colour synesthesia and concomitant dyscalculia.

Here we present the case of SP, a 21-year-old female with life-long dyscalculia. SP was subsequently diagnosed with grapheme-color synesthesia, a diagnosis that serendipitously catalyzed our development of a novel aid:The digit-color calculator (DCC). The DCC substantiates SP's color concurrents, dramatically ameliorating her difficulties with basic calculations. We envisage the DCC and its analogues may assist others in educational settings, particularly if they experience difficulties with the acquisition of literacy and numeracy. Further devices that leverage synesthesia may also have the potential to improve the quality of life for others with trait synesthesia regardless of concomitant disorder.

Motor Memory: Revealing Conditioned Action Tendencies Using Transcranial Magnetic Stimulation.

Action tendencies can be elicited by motivationally salient stimuli (e.g., appetitive rewards) or objects that support utilization behaviors. These action tendencies can benefit behavioral performance through speeded RTs in response tasks and improve detection accuracy in attentional capture tasks. However, action tendencies can be counterproductive when goals change (e.g., refraining from junk foods or abstaining from alcohol). Maintaining control over cue-elicited action tendencies is therefore critical for successful behavior modification. To better understand this relationship, we used transcranial magnetic stimulation to investigate the neural signatures of action tendencies in the presence of previously trained response cues. Participants were presented with a continuous letter stream and instructed to respond quickly to two target letters using two different response keys. Following this training phase, the target letters were embedded in a new task (test phase), and we applied transcranial magnetic stimulation to the motor cortex and measured motor evoked potentials as an index of corticospinal excitability (CSE). We found that CSE could be potentiated by a former response cue trained within a single experimental session, even when participants were instructed to withhold responses during the test phase. Critically, attention to the previously trained response cue was required to elicit the primed modulation in CSE, and successful control of this activity was accompanied by CSE suppression. These findings suggest that well-trained response cues can come to prime a conditioned action tendency and provide a model for understanding how the implementation of cognitive control can override action automaticity.

Semantic repetition blindness and associative facilitation in the identification of stimuli in rapid serial visual presentation.

Repetition blindness (RB) is the inability to detect both instances of a repeated stimulus during rapid serial visual presentation (RSVP). Prior work has demonstrated RB for semantically related critical items presented as pictures, but not for word stimuli. It is not known whether the type of semantic relationship between critical items (i.e., conceptual similarity or lexical association) determines the manifestation of semantically mediated RB, or how this is affected by the format of the stimuli. These questions provided the motivation for the present study. Participants reported items presented in picture or word RSVP streams in which critical items were either low-associate category coordinates (horse-camel), high-associate noncoordinates (horse-saddle), or unrelated word pairs (horse-umbrella). Report accuracy was reduced for category coordinate critical items only when they were presented in pictorial form; accuracy for coordinate word pairs did not differ from that of their unrelated counterparts. Associated critical items were reported more accurately than unrelated critical items in both the picture and word versions of the task. We suggest that semantic RB for pictorial stimuli results from intracategory interference in the visuosemantic space; words do not reliably suffer from semantic RB because they do not necessitate semantic mediation to be reported successfully. Conversely, the associative facilitation observed in both picture and word versions of the task reflects the spread of activation between the representations of associates in the lexical network.

The role of location in visual feature binding.

Location appears to play a vital role in binding discretely processed visual features into coherent objects. Consequently, it has been proposed that objects are represented for cognition by their spatiotemporal location, with other visual features attached to this location index. On this theory, the visual features of an object are only connected via mutual location; direct binding cannot occur. Despite supporting evidence, some argue that direct binding does take over according to task demands and when representing familiar objects. The current study was developed to evaluate these claims, using a brief memory task to test for contingencies between features under different circumstances. Participants were shown a sequence of three items in different colours and locations, and then asked for the colour and/or location of one of them. The stimuli could either be abstract shapes, or familiar objects. Results indicated that location is necessary for binding regardless of the type of stimulus and task demands, supporting the proposed structure. A follow-up experiment assessed an alternate explanation for the apparent importance of location in binding; eye movements may automatically capture location information, making it impossible to ignore and suggesting a contingency that is not representative of cognitive processes. Participants were required to maintain fixation on half of the trials, with an eye tracker for confirmation. Results indicated that the importance of location in binding cannot be attributed to eye movements. Overall, the findings of this study support the claim that location is essential for visual feature binding, due to the structure of object representations.

Motor-evoked potentials reveal functional differences between dominant and non-dominant motor cortices during response preparation.

Transcranial magnetic stimulation (TMS) of the motor cortex produces motor-evoked potentials (MEPs) in contralateral muscles. The amplitude of these MEPs can be used to measure the excitability of the corticospinal tract during motor planning. In two experiments, we investigated learning-related changes in corticospinal excitability as subjects prepared to respond in a choice reaction-time task. Subjects responded with their left or right hand to a left or right arrow, and on some trials the arrow was immediately preceded by a warning cue that signaled which response would be required. TMS was applied to the motor cortex during the warning cues, and MEPs were measured in the dominant or non-dominant hand. We observed changes in corticospinal excitability during the warning cue, but these depended on which hand the subject was preparing to respond with, and how experienced they were with the task. When subjects prepared to respond with the non-dominant hand, excitability increased in the non-dominant hemisphere and decreased in the dominant hemisphere. These changes became stronger with task experience, and were accompanied by behavioral improvements in the task. When subjects were preparing a dominant-hand response, the non-dominant hemisphere was suppressed, but this effect disappeared as subjects gained experience with the task. There were no changes in the dominant hemisphere before dominant-hand responses. We conclude that preparing to respond with the non-dominant hand involves temporarily reversing an asymmetry in excitability that normally favors the dominant hemisphere, and that this pattern is enhanced by learning during the task.

Automatic Recruitment of the Motor System by Undetected Graspable Objects: A Motor-evoked Potential Study.

Previous behavioral and neuroimaging studies have suggested that the motor properties associated with graspable objects may be automatically accessed when people passively view these objects. We directly tested this by measuring the excitability of the motor pathway when participants viewed pictures of graspable objects that were presented during the attentional blink (AB), when items frequently go undetected. Participants had to identify two briefly presented objects separated by either a short or long SOA. Motor-evoked potentials were measured from the right hand in response to a single TMS pulse delivered over the left primary motor cortex 250 msec after the onset of the second target. Behavioral results showed poorer identification of objects at short SOA compared with long SOA, consistent with an AB, which did not differ between graspable and nongraspable objects. However, motor-evoked potentials measured during the AB were significantly higher for graspable objects than for nongraspable objects, irrespective of whether the object was successfully identified or undetected. This provides direct evidence that the motor system is automatically activated during visual processing of objects that afford a motor action.

Summary statistics in the attentional blink.

We used the attentional blink (AB) paradigm to investigate the processing stage at which extraction of summary statistics from visual stimuli ("ensemble coding") occurs. Experiment 1 examined whether ensemble coding requires attentional engagement with the items in the ensemble. Participants performed two sequential tasks on each trial: gender discrimination of a single face (T1) and estimating the average emotional expression of an ensemble of four faces (or of a single face, as a control condition) as T2. Ensemble coding was affected by the AB when the tasks were separated by a short temporal lag. In Experiment 2, the order of the tasks was reversed to test whether ensemble coding requires more working-memory resources, and therefore induces a larger AB, than estimating the expression of a single face. Each condition produced a similar magnitude AB in the subsequent gender-discrimination T2 task. Experiment 3 additionally investigated whether the previous results were due to participants adopting a subsampling strategy during the ensemble-coding task. Contrary to this explanation, we found different patterns of performance in the ensemble-coding condition and a condition in which participants were instructed to focus on only a single face within an ensemble. Taken together, these findings suggest that ensemble coding emerges automatically as a result of the deployment of attentional resources across the ensemble of stimuli, prior to information being consolidated in working memory.

Two scenes or not two scenes: The effects of stimulus repetition and view-similarity on scene categorization from brief displays.

Previous research suggests that understanding the gist of a scene relies on global structural cues that enable rapid scene categorization. This study used a repetition blindness (RB) paradigm to interrogate the nature of the scene representations used in such rapid categorization. When stimuli are repeated in a rapid serial visual presentation (RSVP) sequence (~10 items/sec), the second occurrence of the repeated item frequently goes unnoticed, a phenomenon that is attributed to a failure to consolidate two conscious episodes (tokens) for a repeatedly activated type. We tested whether RB occurs for different exemplars of the same scene category, which share conceptual and broad structural properties, as well as for identical and mirror-reflected repetitions of the same scene, which additionally share the same local visual details. Across 2 experiments, identical and mirror-image scenes consistently produced a repetition facilitation, rather than RB. There was no convincing evidence of either RB or repetition facilitation for different members of a scene category. These findings indicate that in the first 100-150 ms of processing scenes are represented in terms of local visual features, rather than more abstract category-general features, and that, unlike other kinds of stimuli (words or objects), scenes are not susceptible to token individuation failure.

Reconsidering Temporal Selection in the Attentional Blink.

Two episodes of attentional selection cannot occur very close in time. This is the traditional account of the attentional blink, whereby observers fail to report the second of two temporally proximal targets. Recent analyses have challenged this simple account, suggesting that attentional selection during the attentional blink is not only (a) suppressed, but also (b) temporally advanced then delayed, and (c) temporally diffused. Here, we reanalyzed six data sets using mixture modeling of report errors, and revealed much simpler dynamics. Exposing a problem inherent in previous analyses, we found evidence of a second attentional episode only when the second target (T2) follows the first (T1) by more than 100 to 250 ms. When a second episode occurs, suppression and delay reduce steadily as lag increases and temporal precision is stable. At shorter lags, both targets are reported from a single episode, which explains why T2 can escape the attentional blink when it immediately follows T1 (Lag-1 sparing).

Attention is required for the perceptual integration of action object pairs.

Previous studies have demonstrated that functionally related objects are perceptually grouped during visual identification if they are depicted as if interacting with each other (Green and Hummel in J Exp Psychol Hum Percept Perform 32(5):1107-1119, 2006). However, it is unclear whether this integration requires attention or occurs pre-attentively. Here, we used a divided-attention task with variable attentional load to address this question. Participants matched a word label to a target object that was immediately preceded by a briefly presented, task-irrelevant tool that was either functionally related or unrelated to the word label (e.g., axe | "log" or hammer | "log"). The tool was either positioned to interact with the target object or faced away from it. The amount of attention available to process the tool was manipulated by asking participants to make a concurrent perceptual discrimination of varying difficulty on a surrounding frame stimulus. The previously demonstrated advantage for the related-and-interacting condition was replicated under conditions of no or low attentional load. This benefit disappeared under high competing attentional load, indicating that attention is required to integrate functionally related objects together into a single perceptual unit.

Visual field asymmetries in object individuation.

Repetition blindness (RB) is a failure to detect both instances of two identical stimuli presented in close temporal proximity. It is due to an inability to form separate episodic tokens for a repeated stimulus, resulting in a single conscious representation. In three experiments, participants identified two targets presented simultaneously in different spatial locations. These stimuli were either the same or different. In two experiments the targets occurred on either side of fixation, and in a third experiment both were in the same hemifield. In all experiments, RB was more pronounced for stimuli in the right hemifield. In addition, there was a left hemifield advantage for both repeated and non-repeated stimuli when the two stimuli occurred in opposite visual fields and, thus, were processed by different hemispheres. These findings suggest that the right hemisphere plays a dominant role in attentional selection and in creating conscious representations of visual events.

Automaticity and cognitive control in the learned predictiveness effect.

In novel contexts, learning is biased toward cues previously experienced as predictive compared with cues previously experienced as nonpredictive. This is known as learned predictiveness. A recent finding has shown that instructions issued about the causal status of cues influences the expression of learned predictiveness, suggesting that controlled, volitional processes play a role in this effect. Three experiments are reported further investigating the effects of instructional manipulations on learned predictiveness. Experiment 1 confirms the influence of inferential processes, extending previous work to suggest that instructions affect associative memory as well as causal reasoning. Experiments 2 and 3 used a procedure designed to tease apart inferential and automatic contributions to the bias by presenting instructed causes that were previously predictive and previously nonpredictive. The results demonstrate that the prior predictiveness of cues influences subsequent learning over and above the effect of explicit instruction. However, it appears that the relationship between explicit instruction and predictive history is interactive rather than additive. Potential explanations for this interactivity are discussed.