Object-based attention: strength of object representation and attentional guidance

Two or more features belonging to a single object are identified more quickly and more accurately than are features belonging to different objects--a finding attributed to sensory enhancement of all features belonging to an attended or selected object. However, several recent studies have suggested that this "single-object advantage" may be a product of probabilistic and configural strategic prioritizations rather than of object-based perceptual enhancement per se, challenging the underlying mechanism that is thought to give rise to object-based attention. In the present article, we further explore constraints on the mechanisms of object-based selection by examining the contribution of the strength of object representations to the single-object advantage. We manipulated factors such as exposure duration (i.e., preview time) and salience of configuration (i.e., objects). Varying preview time changes the magnitude of the object-based effect, so that if there is ample time to establish an object representation (i.e., preview time of 1,000 msec), then both probability and configuration (i.e., objects) guide attentional selection. If, however, insufficient time is provided to establish a robust object-based representation, then only probabilities guide attentional selection. Interestingly, at a short preview time of 200 msec, when the two objects were sufficiently different from each other (i.e., different colors), both configuration and probability guided attention selection. These results suggest that object-based effects can be explained both in terms of strength of object representations (established at longer exposure durations and by pictorial cues) and probabilistic contingencies in the visual environment.     

Reversing the picture superiority effect: A speed—accuracy trade-off study of recognition memory

Speed-accuracy trade-off methods have been used to contrast single- and dual-process accounts of recognition memory. With these procedures, subjects are presented with individual test items and required to make recognition decisions under various time constraints. In three experiments, we presented words and pictures to be intentionally learned; test stimuli were always visually presented words. At test, we manipulated the interval between the presentation of each test stimulus and that of a response signal, thus controlling the amount of time available to retrieve target information. The standard picture superiority effect was significant in long response deadline conditions (i.e., > or = 2,000 msec). Conversely, a significant reverse picture superiority effect emerged at short response-signal deadlines (< 200 msec). The results are congruent with views suggesting that both fast familiarity and slower recollection processes contribute to recognition memory. Alternative accounts are also discussed.     

Reaction times and electromechanical delay in reactions of increasing and decreasing force

The purpose of this study was to compare reaction times and electromechanical delay between reactions to increase force from rest and reactions to decrease force from an active state in the quadriceps femoris of healthy young adults. Force, position, and electromyographic data were recorded from 35 subjects reacting to a forced knee-flexion perturbation. Electromechanical delay was assessed through cross-correlation of the filtered EMG and force data. Reaction time to increase force (M= 159.9 msec., 95% CI= 149.9-169.9 msec.) was significantly longer than RT to decrease force (M= 124.4 msec., 95% CI= 118.7-130.1 msec.). This difference was partially caused by a difference in electromechanical delay (RT to increase force electromechanical delay was 63 msec., 95% CI=60-67 msec., greater than the RT to decrease force electromechanical delay of 49 msec., 95% CI=46-52 msec.). This difference in reaction time could be important in identifying and interpreting physiologically meaningful changes in muscle force and in intermuscular coordination during movement.     

Varieties of object constancy

Three experiments are described in which two pictures of isolated man-made objects were presented in succession. The subjects' task was to decide, as rapidly as possible, whether the two pictured objects had the same name. With a stimulus-onset asynchrony (SOA) of above 200 msec two types of facilitation were observed: (1) the response latency was reduced if the pictures showed the same object, even though seen from different viewpoints (object benefit); (2) decision time was reduced further if the pictures showed the same object from the same angle of view (viewpoint benefit). These facilitation effects were not affected by projecting the pictures to different retinal locations. Significant benefits of both types were also obtained when the projected images differed in size. However, in these circumstances there was a small but significant performance decrement in matching two similar views of a single object, but not if the views were different. Conversely, the object benefit, but not the viewpoint benefit, was reduced when the SOA was only 100 msec. The data suggest the existence of (at least) two different visual codes, one non-retinotopic but viewer-centred, the other object-centred.     

Phenomenological reports diagnose accuracy of eyewitness identification decisions

This study investigated whether measuring the phenomenology of eyewitness identification decisions aids evaluation of their accuracy. Witnesses (N = 502) viewed a simulated crime and attempted to identify two targets from lineups. A divided attention manipulation during encoding reduced the rate of remember (R) correct identifications, but not the rates of R foil identifications or know (K) judgments in the absence of recollection (i.e., K/[1 − R]). Both RK judgments and recollection ratings (a novel measure of graded recollection) distinguished correct from incorrect positive identifications. However, only recollection ratings improved accuracy evaluation after identification confidence was taken into account. These results provide evidence that RK judgments for identification decisions function in a similar way as for recognition decisions; are consistent with the notion of graded recollection; and indicate that measures of phenomenology can enhance the evaluation of identification accuracy.     

A diffusion model account of response time and accuracy in a brightness discrimination task: fitting real data and failing to fit fake but plausible data

A brightness discrimination experiment was performed to examine how subjects decide whether a patch of pixels is “bright” or “dark,” and stimulus duration, brightness, and speed versus accuracy instructions were manipulated. The diffusion model (Ratcliff, 1978) was fit to the data, and it accounted for all the dependent variables: mean correct and error response times, the shapes of response time distributions for correct and error responses, and accuracy values. Speed-accuracy manipulations affected only boundary separation (response criteria settings) in the model. Drift rate (the rate of accumulation of evidence) in the diffusion model, which represents stimulus quality, increased as a function of stimulus duration and stimulus brightness but asymptoted as stimulus duration increased from 100 to 150 msec. To address the argument that the diffusion model can fit any pattern of data, simulated patterns of plausible data are presented that the model cannot fit.     

Color diagnosticity in object recognition

Does color influence object recognition? In the present study, the degree to which an object was associated with a specific color was referred to ascolor diagnosticity. Using a feature listing and typicality measure, objects were identified as either high in color diagnosticity or low in color diagnosticity. According to the color diagnosticity hypothesis, color should more strongly influence the recognition of high color diagnostic (HCD) objects (e.g., a banana) than the recognition of low color diagnostic (LCD) objects (e.g., a lamp). This prediction was supported by results from classification, naming, and verification experiments, in which subjects were faster to identify color versions of HCD objects than they were to identify achromatic versions and incongruent color versions. In contrast, subjects were no faster to identify color versions of LCD objects than they were to identify achromatic and incongruent color versions. Moreover, when shape information was degraded but color information preserved, subjects were less impaired in their recognition of degraded HCD objects than of degraded LCD objects, relative to their nondegraded versions. Collectively, these results suggest that color plays a role in the recognition of HCD objects.     

Effects of instantaneous object input and past experience on object-based attention

Evidence for object-based attention typically comes from studies using displays with unchanged objects, and no consensus has yet been reached as to whether the object effect would be altered by changing object displays or having seen this change across-trials. We examined this by using modifications of the double-rectangle cuing paradigm of Egly et al. [Egly, R., Driver, J., & Rafal, R. D. (1994). Shifting visual attention between objects and locations: Evidence from normal and parietal lesion subjects. Journal of Experimental Psychology: General, 123, 161-177], and our results, when the objects remained unchanging, replicated the original object effect. However, no object effect was found when the rectangles disappeared from view in the last (target) frame. This was true regardless of the likelihood of the rectangles disappearing, indicating the importance of instantaneous object inputs for object-based attention. The across-trial experience of seeing a different object (boomerang), however, was found to influence the object effect when the cued rectangles persisted throughout the trial. Unlike previous studies, which emphasize one or the other, we demonstrate clearly that instantaneous object inputs and past experience interact to determine the way attention selects objects.     

Orientation invariance in visual object priming depends on prime-target asynchrony

Two experiments are reported in which orientation effects on visual object recognition latency were examined. In Experiment 1, we assessed picture-naming performance as a function of image-plane stimulus orientation and found increasing response times with increased misorientation of the stimulus. In Experiment 2, we examined the repetition priming effect on the identification of upright targets as a function of prime orientation. With time delays of 100, 200, or 500 msec between the onset of the prime and that of the target (i.e., stimulus onset asynchrony [SOA]), the magnitude of the priming effect decreased with increasing misorientation of the prime. These results contrast with the orientation-invariant priming effects reported in some previous repetition priming studies. These investigations all used relatively long prime-target SOAs. Confirming the crucial role of the latter variable, Experiment 2 shows that the magnitude of the repetition priming effect is invariant across prime orientations with an SOA of 1,000 msec. The possible implications of the present observations with respect to the issue of orientation invariance versus dependency of the visual object recognition processare discussed.     

Independent effects of colour on object identification and memory

We examined the effects of colour on object identification and memory using a study–test priming procedure with a coloured-object decision task at test (i.e., deciding whether an object is correctly coloured). Objects were selected to have a single associated colour and were either correctly or incorrectly coloured. In addition, object shape and colour were either spatially integrated (i.e., colour fell on the object surface) or spatially separated (i.e., colour formed the background to the object). Transforming the colour of an object from study to test (e.g., from a yellow banana to a purple banana) reduced priming of response times, as compared to when the object was untransformed. This utilization of colour information in object memory was not contingent upon colour falling on the object surface or whether the resulting configuration was of a correctly or incorrectly coloured object. In addition, we observed independent effects of colour on response times, whereby coloured-object decisions were more efficient for correctly than for incorrectly coloured objects but only when colour fell on the object surface. These findings provide evidence for two distinct mechanisms of shape–colour binding in object processing.     

Prehension in children and adults: The effects of object size

Studies of visually goal-directed arm movements in adults have shown that various task constraints such as intention, context, and object properties affect different kinematic characteristics of the movement components (Jeannerod, 1984; MacKenzie et al., 1987; Marteniuk et al., 1987, 1990; Paulignan et al., 1991; Soechting, 1984). The purpose of the present study was to compare the effects of varying object size on the kinematics of reaching and grasping in both children and adults. Five children aged 9–10 years and five adults aged 18–24 years reached for and grasped three different sized cubes. Results revealed that object size had the same effect on the planning and control of reaching and grasping movements in children as in adults. Unlike adults, however, children in this age range spent more time in deceleration and reached peak aperture much later in the movement trajectory. The results were interpreted as immature integration of the visual and proprioceptive systems in 9–10 year olds. The implications of these findings for further examining developmental trends in prehension are discussed.PsycINFO classification: 2330     

Attention demands of visual search

The relation between attention demand and the number of items in the array (array size) was investigated by engaging subjects in a primary search task and measuring spare capacity at different points in time, with a secondary tone task that occurred randomly on half of the trials. The major variables in both tasks were array size 14, 8, or 12 letters and stimulus onset asynchrony (SOA: ?400, ?200, 0, 200, 400, and 600 msec. Subjects were able to perform the tasks quite independently, and me, st of the interference that resulted from nonindependence appeared in tone-task performance. Theamount of interference (i.e., maximum tone reaction time) was independent of array size, but theduration of interference (li.e., the number of SOAs at which tone reaction time was elevated) increased with array size. The findings were interpreted as supporting unlimited-capacity models of visual search performance.     

Dorsal stream activation during retrieval of object size and shape

We investigated dorsal visual stream involvement in the retrieval of a variety of visual attributes of common objects, using functional magnetic resonance imaging. Seven subjects made binary decisions about the shape, color, and size of named objects during scanning. Bilateral parietal activity was significantly greater during retrieval of shape and size information than during retrieval of color information. Consistent with a domain-specific distributed model of semantic organization, the finding that dorsal stream activity is associated with size and shape retrieval, as compared with color retrieval, may indicate that both size and shape information are learned partly through dorsally mediated processes, such as visually guided grasping. These results demonstrate that both visual-processing streams (i.e., the ventral “what” pathway and the dorsal “where” pathway) are involved in the storage and/or retrieval of knowledge of object appearance but that, just as in vision, these two pathways may play different roles in conceptual processing.     

The effects of object weight on the kinematics of prehension

The purpose of these experiments was to determine the effects of object weight and condition of weight presentation on the kinematics of human prehension. Subjects performed reaching and grasping movements to metal dowels whose visible characteristics were similar but whose weight varied (20, 55, 150, 410 g). Movements were performed under two conditions of weight presentation, random (weight unknown) and blocked (weight known). Three-dimensional movements of the thumb, index finger, and wrist were recorded, using a WATSMART system to obtain information regarding the grasp and transport components. The results of the first experiment indicated that object weight and condition of presentation affected the temporal and kinematic measures for both the grasp and transport components. In conjunction with the results of a second experiment, in which time in contact with the dowel was measured, it was shown that the free-motion phase of prehension (i.e., up to object contact) was invariant over the different conditions, however. The changes were observed in the finger-object interaction phase (when subjects applied forces after contact with the dowel), prior to lift-off. These results were interpreted as indicating (a) object weight does not influence the planning and execution of the free-motion phase of prehension and (b) there are at least two motor control phases involved in prehension, one for making contact with the object and the other for finger-object interaction. The changing contributions of visual, kinesthetic, and haptic information during these two phases is discussed.     

Color makes a difference: two-dimensional object naming in literate and illiterate subjects

Previous work has shown that illiterate subjects are better at naming two-dimensional representations of real objects when presented as colored photos as compared to black and white drawings. This raises the question if color or textural details selectively improve object recognition and naming in illiterate compared to literate subjects. In this study, we investigated whether the surface texture and/or color of objects is used to access stored object knowledge in illiterate subjects. A group of illiterate subjects and a matched literate control group were compared on an immediate object naming task with four conditions: color and black and white (i.e., grey-scaled) photos, as well as color and black and white (i.e., grey-scaled) drawings of common everyday objects. The results show that illiterate subjects perform significantly better when the stimuli are colored and this effect is independent of the photographic detail. In addition, there were significant differences between the literacy groups in the black and white condition for both drawings and photos. These results suggest that color object information contributes to object recognition. This effect was particularly prominent in the illiterate group.     

Negative priming without reaction time: Effects on identification of masked letters

Responses to an object are often slower and/or less accurate if that object is related to a recently ignored object. Thisnegative priming effect has previously been examined only in reaction time tasks. In the present experiment, target letters and flanking distractor letters were displayed for 33, 100, or 300 msec, followed by a pattern mask. Subjects attempted to identify the target letters, with no demand for speed. Identification accuracy was reduced for targets that matched distractors presented on the immediately preceding trial. However, there was no bias against reporting preceding distractors on catch trials with no presented target. Implications for theories of negative priming are discussed.     

Auditory apparent motion in the free field: The effects of stimulus duration and separation

The effects of stimulus duration and spatial separation on the illusion of apparent motion in the auditory modality were examined. Two narrow-band noise sources (40 dB, A-weighted) were presented through speakers separated in space by 2.5°, 5°, or 100, centered about the subject’s midline. The duration of each stimulus was 5, 10, or 50 msec. On each trial, the sound pair was temporally separated by 1 of 10 interstimulus onset intervals (ISOIs): 0, 2, 4, 6, 8, 10, 15, 20, 50, or 70 msec. Five subjects were tested in nine trial blocks; each block represented a particular spatial-separation-duration combination. Within a trial block, each ISOI was presented 30 times each, in random order. Subjects were instructed to listen to the stimulus sequence and classify their perception of the sound into one of five categories: single sound, simultaneous sounds, continuous motion, broken motion, or successive sounds. Each subject was also required to identify the location of the first-occurring stimulus (left or right). The percentage of continuous-motion responses was significantly affected by the ISOI [F(9,36) = 5.67,p < .001], the duration × ISOI interaction [F(18,72) = 3.54,p < .0001], and the separation × duration × ISOI interaction [F(36,144) = 1.51,p < .05]. The results indicate that a minimum duration is required for the perception of auditory apparent motion. Little or no motion was reported at durations of 10 msec or less. At a duration of 50 msec, motion was reported most often for ISOIs of 20–50 msec. The effect of separation appeared to be limited to durations and-ISOIs during which little motion was perceived.     

Resolving competition when naming an object in a multiple-object display

Naming an object in the context of other objects requires the selection and processing of the target object at different levels, while the processing of competing representations activated by context objects has to be constrained. At what stage are these competing representations attenuated? To address this question, we presented pairs of target and context objects that were either similar in visual shape (e.g., umbrella–palm tree) or dissimilar in visual shape (e.g., umbrella–ladder), so that the context object would attract various amounts of attention. The activation of the context object at different levels of processing was assessed by means of auditory distractors (semantically related, or phonologically related, or unrelated to the context object). Semantic and phonological distractor effects were observed for shape-related object pairs, but not for unrelated object pairs. This finding suggests that context objects do not activate their associated lexical representations to any substantial amount, unless they capture attention. In that case, they undergo full lexical processing up to a phonological level. Implications for models of word production are discussed.