Correspondence problems cause repositioning costs in visual working memory

Visual working memory performance often declines when objects are tested in new positions from those they were observed. We report an asymmetry in repositioning costs for orientation compared to colour memory (Experiment 1). Follow-up experiments demonstrated a similar asymmetry for line length memory compared to shape memory (Experiment 2). When different shades of the same colour category were used, however, repositioning costs emerged for colour as well (Experiment 3). Finally, a direct comparison experiment demonstrated an asymmetry for orientation compared to categorical colours, but in a task with no explicit memory demands (Experiment 4). These results challenge previous accounts of repositioning costs, suggesting that they emerge not due to the contents of visual working memory, but naturally because of correspondence procedures that must be executed in order to use a memory to judge the present.     

The pigeon's discrimination of shape and location information

Two groups of pigeons (n = 4) were trained with 16 line drawings portraying a fixed shape and a variable shape. The four variable shapes (a wedge, a cone, a cylinder, and a handle) appeared to the left of, to the right of, above, or below the fixed shape (a cube). Group Shape (S) was required to discriminate the identity of the variable shape that was mated with the cube, whereas Group Location (L) was required to discriminate where the variable shape appeared relative to the cube. Three of the four pigeons in each group mastered their respective tasks. Later tests revealed that the two groups of pigeons had attended to different aspects of the shape pairs, even though the visual stimuli and general procedures they had been given were the same. Group S had attended to the identity of the variable shape and had ignored the identity and location of the cube, whereas Group L had attended to the configuration of the two shapes. The methods and stimuli could be useful in delineating the biological bases of shape and location perception.     

Accurate identification but no priming and chance recognition memory for pictures in RSVP sequences

In 1969, Potter and Levy reported that recognition memory of accurately perceived RSVP pictures was extremely low, an effect that they attributed to disruption of memory consolidation. Here we report that the repetition of an RSVP picture (72-126 msec/picture) up to 31 times prior to when it became a target had no effect on identification accuracy. At these rates, forced-choice recognition memory was at chance. Single presentations of the pictures outside of the RSVP sequences readily resulted in substantial priming of their identification within the sequences. We offer a neural interpretation of Potter and Levy's explanation, as well as contemporary two-stage accounts of RSVP memory and attentional phenomena, based on the recent finding (Tovee & Rolls, 1995) that most of the information in inferior temporal cells is conveyed in the first 50msec of firing but the cells continue their activity for an additional 350msec. The additional activity, by our account, is required for memory and it is this activity that may be disrupted by attention to the next image during RSVP presentations. The critical factor for priming, if not memory in general, may be attention to the stimulus for a few hundred milliseconds beyond that required for its identification. Single-trial presentations thus manifest robust memory and priming effects - even when the stimulus cannot be identified - whereas RSVP conditions in which the stimulus can be identified result in poor memory.     

Culture and facial expressions of emotion

With over a century of theoretical developments and empirical investigation in broad fields (e.g., anthropology, psychology, evolutionary biology), the universality of facial expressions of emotion remains a central debate in psychology. How near or far, then, is this debate from being resolved? Here, I will address this question by highlighting and synthesizing the significant advances in the field that have elevated knowledge of facial expression recognition across cultures. Specifically, I will discuss the impact of early major theoretical and empirical contributions in parallel fields and their later integration in modern research. With illustrative examples, I will show that the debate on the universality of facial expressions has arrived at a new juncture and faces a new generation of exciting questions.     

On the depth reversibility of point-light actions

We investigate the occurrence of perspective reversals for a depth-ambiguous point-light figure. In addition, we exploit the phenomenon of reversibility to search for stimulus features relevant in the process of depth assignment. Experiment 1 shows that perceptual switches indeed occur during prolonged viewing, although the switches occur infrequently. The reversibility is confirmed in Experiment 2, in which the perceptual ambiguity of the point-light action is manipulated as well as observers’ intention to perceive a particular alternative. In addition, the pattern of eye movements reveals local stimulus features specifically associated with the perception of the different alternatives. In Experiment 3, the importance of these features as determining factors of the initial interpretation is investigated by manipulating the location of the first fixation on the stimulus. Implications for a better understanding of biological motion perception are discussed.     

New insights on eye blindness and hand sight: Temporal constraints of visuo-motor networks

Pioneer experiments on saccadic suppression have shown that this effect is not followed by motor disorientation: Conscious perception of a target displacement can be dissociated from correct manual target reaching. It has subsequently been demonstrated that movement corrections with the same latency and spatial characteristics can be produced in conditions allowing perceptual awareness of perturbation of a target as in condition inducing saccadic suppression. In addition to the qualitative dissociation between motor performance and conscious awareness, quantitative temporal dissociations in action can be observed by manipulating different features of the visual target. When the target of an ongoing simple action is perturbed, a temporal advantage is found for responses to perturbations of location relative to colour and shape. Furthermore, there seems to be a temporal advantage for automatic motor corrections made in response to a target displacement as compared to other responses (other ongoing movement adjustments, movement interruption, conditional motor response such as pressing a key, verbal response, delayed matching-to-sample tasks). Thus, this paper reviews evidence for the fact that the temporal characteristics of any given response to a stimulus are dependent both on the sensory processes and on the type of response generated. Accordingly, identification responses (such as verbal report) to a visual stimulus are much slower than motor corrections of an ongoing movement in response to a target location change because of different processing times of the stimulus features (“What” compared to “Where”) and of the response itself (“What” compared to “How”). The existence of two continua (What/Where and What/How) is proposed between these two extreme stimulus- response combinations. This model may be a useful framework to better understand visuo-motor transformations and the network of connections between visual and motor areas.     

Prevalence-based decisions undermine visual search

In visual search, observers make decisions about the presence or absence of a target based on their perception of a target during search. The present study investigated whether decisions can be based on observers’ expectation rather than perception of a target. In Experiment 1, participants were allowed to make target-present responses by clicking on the target or, if the target was not perceived, a target-present button. Participants used the target-present button option more frequently in difficult search trials and when target prevalence was high. Experiment 2 and 3 employed a difficult search task that encouraged the use of prevalence-based decisions. Target presence was reported faster when target prevalence was high, indicating that decisions were, in part, cognitive, and not strictly perceptual. A similar pattern of responses were made even when no targets appeared in the search (Experiment 3). The implication of these prevalence-based decisions for visual search models is discussed.     

Is attention necessary for perceiving gaze direction? It depends on how you look at it: Evidence from the locus-of-slack method

Several researchers have studied how we process and perceive gaze direction. However, it is still unclear at which perceptual stage of gaze processing (encoding or/and categorization), attention is required to judge gaze direction. We report a study in which we manipulated the difficulty of gaze perceptual judgements (easy vs. difficult) and used the locus-of-slack method to test the role of different types of attention (spatial and central) in the encoding and categorization of gaze direction. In Experiment 1 we used the spatial cueing paradigm to investigate if gaze direction judgements can be carried out while spatial attention is diverted. In Experiment 2 we used the psychological refractory period (PRP) paradigm to determine whether judgement of gaze direction involves central attention processes. The findings demonstrate that gaze judgements require input attention (both for the encoding and categorization stage) but not central attention. The implications of the results are discussed.     

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.