Target-background Similarity Research Articles

Neural correlates of perceptual similarity masking in primate V1.

Visual detection is a fundamental natural task. Detection becomes more challenging as the similarity between the target and the background in which it is embedded increases, a phenomenon termed 'similarity masking'. To test the hypothesis that V1 contributes to similarity masking, we used voltage sensitive dye imaging (VSDI) to measure V1 population responses while macaque monkeys performed a detection task under varying levels of target-background similarity. Paradoxically, we find that during an initial transient phase, V1 responses to the target are enhanced, rather than suppressed, by target-background similarity. This effect reverses in the second phase of the response, so that in this phase V1 signals are positively correlated with the behavioral effect of similarity. Finally, we show that a simple model with delayed divisive normalization can qualitatively account for our findings. Overall, our results support the hypothesis that a nonlinear gain control mechanism in V1 contributes to perceptual similarity masking.

Neural correlates of perceptual similarity masking in primate V1

Visual detection is a fundamental natural task. Detection becomes more challenging as the similarity between the target and the background in which it is embedded increases, a phenomenon termed ‘similarity masking’. To test the hypothesis that V1 contributes to similarity masking, we used voltage sensitive dye imaging (VSDI) to measure V1 population responses while macaque monkeys performed a detection task under varying levels of target-background similarity. Paradoxically, we find that during an initial transient phase, V1 responses to the target are enhanced, rather than suppressed, by target-background similarity. This effect reverses in the second phase of the response, so that in this phase V1 signals are positively correlated with the behavioral effect of similarity. Finally, we show that a simple model with delayed divisive normalization can qualitatively account for our findings. Overall, our results support the hypothesis that a nonlinear gain control mechanism in V1 contributes to perceptual similarity masking.

Concealed multiscale feature extraction network for automatic four-bar target detection in infrared imaging

The measurement of the minimum temperature difference (MTD) at which a four-bar target can be resolved is an important task for assessing the performance of infrared imaging equipment. Recently, there have been efforts to use an automatic objective approach based on machine learning to replace the classical manual subjective MTD measurement approach, which is heavily influenced by the psychological subjective factors of the operator and is limited in accuracy and processing speed. However, the scale variability of the four-bar targets and the high intrinsic target-background similarity in infrared images have been observed to present a challenging problem for automatic MTD measurement. We present a concealed multiscale feature extraction network (CMF-Net), a backbone for automatic multiscale four-bar target detections, in an attempt to address the aforementioned challenges. We first propose a multilevel feature pyramid module to construct a robust representation of multiscale four-bar targets. Next, to distinguish between the four-bar targets from the background, a target saliency enhancement module (TSE) is introduced to capture discriminative features about the target by encoding local and global contextual information. Experiments show that the proposed method is effective and achieves state-of-the-art four-bar target detection results on infrared-image dataset compared with existing methods.

Spatial structure, phase, and the contrast of natural images.

The sensitivity of the human visual system is thought to be shaped by environmental statistics. A major endeavor in vision science, therefore, is to uncover the image statistics that predict perceptual and cognitive function. When searching for targets in natural images, for example, it has recently been proposed that target detection is inversely related to the spatial similarity of the target to its local background. We tested this hypothesis by measuring observers’ sensitivity to targets that were blended with natural image backgrounds. Targets were designed to have a spatial structure that was either similar or dissimilar to the background. Contrary to masking from similarity, we found that observers were most sensitive to targets that were most similar to their backgrounds. We hypothesized that a coincidence of phase alignment between target and background results in a local contrast signal that facilitates detection when target-background similarity is high. We confirmed this prediction in a second experiment. Indeed, we show that, by solely manipulating the phase of a target relative to its background, the target can be rendered easily visible or undetectable. Our study thus reveals that, in addition to its structural similarity, the phase of the target relative to the background must be considered when predicting detection sensitivity in natural images.

Training detection of camouflaged targets in natural scenes: Backgrounds and targets both matter

As target-background similarity increases, search performance declines, but this pattern can be attenuated with training. In the present study we (1) characterized training and transfer effects in visual search for camouflaged targets in naturalistic scenes, (2) evaluated whether transfer effects are preserved 3 months after training, (3) tested the suitability of the perceptual learning hypothesis (i.e., using learned scene statistics to aid camouflaged target detection) for explaining camouflage search improvements over training, and (4) provide guidance for camouflage detection training in practice. Participants were assigned to one of three training groups: adaptive camouflage (difficulty varied by performance), massed camouflage (difficulty increased over time), or an active control (no camouflage), and trained over 14 sessions. Additional sessions measured transfer (immediately post training) and retention of training benefits (10 days and 3 months post training). Both the adaptive and massed training groups showed improved camouflaged target detection up to 3 months following training, relative to the control. These benefits were observed only with backgrounds and targets that were similar to those experienced during training and are broadly consistent with the perceptual learning hypothesis. In practice, training interventions should utilize stimuli similar to the operational environment in which detection is expected to occur.

Spatial resolution and object segmentation efficiency constrain grouping effects in attentive tracking

Previous studies of multiple object tracking suggested that spatiotemporal features (e.g., speed, direction, location) and surface features (e.g., color, shape, size) can guide perceptual grouping. However, it is still unclear how target-distractor distinctiveness and target-background similarity affect grouping effects in attentive tracking. To address these two questions, three experiments have been carried out in the current study. In Experiment 1, we manipulated the target-distractor distinctiveness and found that tracking performance logarithmically improved when the target-distractor distinctiveness linearly increased. In Experiment 2a and 2b, we varied the target-background similarity and found that too high or too low target-background similarity damaged the tracking performance, while only the middle target-background similarity resulted in the best tracking performance. These findings reveal that not only target-distractor distinctiveness but also target-background similarity plays a vital role in guiding the attention of perceptual grouping in attentive tracking. The guidance induced by target-distractor distinctiveness is constrained by the spatial resolution, while the guidance induced by target-background similarity is constrained by the efficiency of object segmentation. Additionally, our results showed that tracking capacity varied with the target-distractor distinctiveness and the target-background similarity, even though the number of targets being tracked was fixed. It suggests that there may be a trade-off between the difficulty of tracking and the number of targets that can be tracked. Thus, tracking capacity is more likely to be limited by the flexible attention resources rather than the number of fixed slots.

Developing and Evaluating a Target-Background Similarity Metric for Camouflage Detection

BackgroundMeasurement of camouflage performance is of fundamental importance for military stealth applications. The goal of camouflage assessment algorithms is to automatically assess the effect of camouflage in agreement with human detection responses. In a previous study, we found that the Universal Image Quality Index (UIQI) correlated well with the psychophysical measures, and it could be a potentially camouflage assessment tool.MethodologyIn this study, we want to quantify the camouflage similarity index and psychophysical results. We compare several image quality indexes for computational evaluation of camouflage effectiveness, and present the results of an extensive human visual experiment conducted to evaluate the performance of several camouflage assessment algorithms and analyze the strengths and weaknesses of these algorithms.SignificanceThe experimental data demonstrates the effectiveness of the approach, and the correlation coefficient result of the UIQI was higher than those of other methods. This approach was highly correlated with the human target-searching results. It also showed that this method is an objective and effective camouflage performance evaluation method because it considers the human visual system and image structure, which makes it consistent with the subjective evaluation results.

Visual search for real world targets under conditions of high target–background similarity: Exploring training and transfer in younger and older adults

Real world visual search tasks often require observers to locate a target that blends in with its surrounding environment. However, studies of the effect of target–background similarity on search processes have been relatively rare and have ignored potential age-related differences. We trained younger and older adults to search displays comprised of real world objects on either homogenous backgrounds or backgrounds that camouflaged the target. Training was followed by a transfer session in which participants searched for novel camouflaged objects. Although older adults were slower to locate the target compared to younger adults, all participants improved substantially with training. Surprisingly, camouflage-trained younger and older adults showed no performance decrements when transferred to novel camouflage displays, suggesting that observers learned age-invariant, generalizable skills relevant for searching under conditions of high target–background similarity. Camouflage training benefits at transfer for older adults appeared to be related to improvements in attentional guidance and target recognition rather than a more efficient search strategy.

Searching for camouflaged targets: Effects of target-background similarity on visual search

Do observers search for camouflaged targets by looking through the distractors or by scrutinizing the target-similar background? In four experiments observers searched for toy targets among distractors under varying set size and target-background similarity (TBS) conditions. Manual errors and RTs increased with TBS, although search slopes did not significantly differ. Eye movement analyses revealed that the majority of fixations fell on discrete distractors rather than on the target-similar background, even under high TBS conditions. These data suggest a biased search process; salient patterns segmented from a background are preferred while more target-similar unsegmented regions of the background are relatively neglected.

The Relation between Target Localisation in Strings of Letters, Contrast, and Refresh Rate

Jacobs (1987, Vision Research27 1953 – 1966) obtained psychometric curves to investigate the relationship between target localisability and the latency of primary saccades. These psychometric curves show correct scores as a function of string length, target location, and target-background similarity. They were obtained with white text on a black background. We repeated this experiment, with a few extensions. First, we did not only use white text on a black background, but we used black text on a white background as well. The stimuli were also presented with the use of isoluminant colours. Second, we varied the refresh rate of the screen (from 60 Hz up to 150 Hz). Third, we used two different instructions for the subjects: in one the subject was instructed to indicate the position of the target relative to the beginning of the string; in the other the position of the target relative to the fixation point. When the string was presented to the right of the fixation point, the results of these two instructions were predicted to be similar; in the other case the results might be different. The results of our experiments show a clear effect of the amount of contrast between text and background, and an influence of the screen refresh rate. We also found that the results differ depending on the instruction used. Sadly, we were not able to replicate all of the results of the original experiment by Jacobs.

Towards a resolution theory of visual attention

Abstract The present paper proposes that preattended visual information produces a coarse representation by automatically stimulating a detector that responds to a range of similar features. Directing attention to a given location improves the resolution of features by computing the relative activation of overlapping internal detectors. A selective review of the literature shows that the proposed distinction is supported by a variety of studies investigating diverse phenomena of target-background similarity effects, conjunctive search, illusory conjunctions, feature similarity effects, global precedence, shape discrimination, detection of signals, categorical search, curvature discrimination, and length perception.

Visual search along the colour dimension.

Subjects searched for a chromatic target among coloured background items. With low target-background chromatic similarity, response latencies remained uniformly short whether the target was present or not and whether the items were chromatically homogeneous or not. Latencies increased with increases in target-background similarity and were longest with heterogeneous backgrounds, with which the effects of trial also became manifest. We employed Treisman's model of visual search to account for these findings. In particular, we suggest that similarity increases forced a shift from a preattentive to an attentive search, the latter being importantly shaped by the background's level of chromatic variance.

Spatial and/or temporal adjustments of scanning behavior to visibility changes

This paper continues a series of studies focussing on elementary processes controlling eye movements in visual search and reading. It investigates the question of how scanning behavior in a letter search task adjusts to changes in spatial visibility created by different visual factors, such as viewing distance, inter-letter spacing and target-background similarity. Each of the three visual factors is found to affect scanning behavior in a different way, either by changing its spatial parameter (saccade size) or its temporal (fixation duration), or both of them at the same time. Possible mechanisms underlying these effects are discussed.

Eye-movement control in visual search: how direct is visual span control?

In order to distinguish between the effects of low-level sensory mechanisms and those of higher level factors on eye-movement control processes, a simple letter search task was used in which cognitive load was reduced to the very minimum. The special purpose of this study was to test the visual span control hypothesis, which considers that, in such a task, eye movements are controlled as a direct function of spatial visibility limits (O’Regan, Levy-Schoen, & Jacobs, 1983). In a first psychophysical experiment, three methods were used to manipulate the spatial visibility limits (visual span), as measured by a psychophysical procedure: changing viewing distance, interletter spacing, and target-background similarity. The results of this experiment then were used as a reference for predicting mean saccade sizes and fixation durations in a visual search task in which the same visibility changes were made. About 80% of the variance of mean saccade sizes could be accounted for by adjustment of saccades to changes in visual span, so the visual span control hypothesis was confirmed. As to the temporal characteristics of scanning behavior, less than 50% of fixation duration variance seemed to be determined by visual span changes. Other, higher level factors, possibly related to decisional processes intervening in the triggering of saccades and the computation of their spatial parameters, might play an important role in determining fixation durations in a simple search task. The results are interpreted in relation to recent models of eye-movement control by two largely independent subsystems functioning in parallel.

Visual search through color displays: effects of target-background similarity and background uniformity.

The effects of target-background similarity and background uniformity were investigated in two experiments in which subjects reported the presence or absence of an achromatic target item in arrays containing irrelevant chromatic items. In Experiment 1, both “present” and “absent” decision times were an increasing function of the similarity of a predefined target item to the background, and were shortened when the interitem similarity of the background set was increased. In Experiment 2, the effects of target-background similarity on the “present” decision were replicated when subjects were not informed on each trial as to which member of the target set might appear in the array, and the “absent” decision was faster when each row of the array comprised background items of a single color than when these items were allocated randomly to array locations. The results are interpreted in terms of the role of pre-attentive grouping operations.

Effects of cued-set spatial arrangement and target-background similarity in the partial-report paradigm

In previous studies of selective attention using the Sperling partial-report paradigm, the selection criterion has been confounded with the spatial arrangement of the cued items, and target-background similarity has varied concommitantly. In this partial-report experiment, subjects are directed to report the identities of five red letters embedded in a 5 × 5 matrix. With selection criterion thus held constant, the arrangement of the cued items and the nature of the background material are varied. Both arrangement and background effects are highly significant, as is the interaction between them. Some constraints on models of visual selective attention are discussed.