Karla Evans | Harvard University (original) (raw)
Papers by Karla Evans
Abstract Diagnostic accuracy for radiologists is above that expected by chance when they are expo... more Abstract Diagnostic accuracy for radiologists is above that expected by chance when they are exposed to a chest radiograph for only one-fifth of a second, a period too brief for more than a single voluntary eye movement. How do radiologists glean information from a first glance at an image? It is thought that this expert impression of the gestalt of an image is related to the everyday, immediate visual understanding of the gist of a scene. Several high-speed mechanisms guide our search of complex images.
Abstract A typical visual scene we encounter in everyday life is complex and filled with a huge a... more Abstract A typical visual scene we encounter in everyday life is complex and filled with a huge amount of perceptual information. The term,'visual attention'describes a set of mechanisms that limit some processing to a subset of incoming stimuli. Attentional mechanisms shape what we see and what we can act upon. They allow for concurrent selection of some (preferably, relevant) information and inhibition of other information. This selection permits the reduction of complexity and informational overload.
Abstract The ability to detect relationships between different sensory events grants behavioral f... more Abstract The ability to detect relationships between different sensory events grants behavioral flexibility, permitting the substitution of one sensory channel for another as well as the integration of information from different sensory streams. Studies in this dissertation examine the featural correspondence between basic auditory and visual features, exploring the nature, the neural correlates and the role of attention in their interaction.
Journal of Vision, Jan 1, 2010
Abstract Observers can report some semantic content of scenes when those scenes are presented for... more Abstract Observers can report some semantic content of scenes when those scenes are presented for 20 msec, flanked in time by masks. It is likely that only a single object could be selected for attentional processing in this time so this gist processing would seem to involve non-selective processing of the entire image. Similarly, we find that expert observers (radiologists and cytopathologists) can detect subtle signs of cancer at above chance levels in 250 msec exposures of mammograms and Pap-smears. These exposures are ...
Journal of Vision, Jan 1, 2004
Abstract How much is possible outside the focus of attention? Recent studies have argued that per... more Abstract How much is possible outside the focus of attention? Recent studies have argued that perception of natural scenes contradicts common findings of limited capacity of visual attention. They have shown that participants detect a natural category target in real scenes, just as well in a dual task situation as when the scene receives full attention (Li et al. 2002). Furthermore they are able to search two scenes in parallel in a go-no-go natural category detection task (Rousselet et al. 2002). We believe that this ability may not be due to high- ...
Journal of Vision, Jan 1, 2006
Abstract The brain derives information from several sense modalities to enhance the speed and acc... more Abstract The brain derives information from several sense modalities to enhance the speed and accuracy of detection of objects and events, and the choice of appropriate responses. There is mounting evidence that perceptual experiences that may appear to be modality specific are also influenced by activity from other sensory modalities, even in the absence of awareness of this interaction. In a series of speeded classification tasks we found natural spontaneous mappings between the pitch of sounds and the visual features of vertical ...
Journal of Vision, Jan 1, 2009
Abstract It has been well documented that people are able to get some semantic and/or statistical... more Abstract It has been well documented that people are able to get some semantic and/or statistical information out of a briefly presented image. They are able to report on the gist of a scene in 100 ms (Potter, 1975), detect the presence of an animal in an image presented for 20 ms (Thorpe et al., 1996) and determine the mean size of sets of objects (Ariely, 2001; Chong & Treisman, 2003). These findings suggest that some advanced scene processing is possible without attentional selection of specific objects. What are the limits on this non- ...
Wiley Interdisciplinary Reviews: …, Jan 1, 2011
Quantity or numerosity is one of the basic properties of our environment. Humans and animals both... more Quantity or numerosity is one of the basic properties of our environment. Humans and animals both have the neural representation of quantity or "number sense". The ability to extract and to manipulate numbers is closely related to our various cognitive functions such as the capacity of working memory, mathematical achievement, and texture perception. Evidence shows that the sense of number is not a unitary mechanism but rather a composition of two distinct processes; enumeration and estimation. The review examines how numerosity is represented in the visual domain and its relation to different modes of attention. Enumeration or counting permits an exact representation of a distinct number of objects, with an awareness of each object achieved through focal deployment of attention to each object serially. On the other hand, estimation involves an approximation of the number of different items or a sense of ensemble statistics, achieved through fast deployment of distributed attention over a set of objects as a whole. In this overview we suggest that a focused attention mode is more suitable for enumeration, whereas a distributed attention mode is better for estimation.
Psychonomic bulletin & …, Jan 1, 2011
Numerous studies have shown that musicians outperform nonmusicians on a variety of tasks. Here we... more Numerous studies have shown that musicians outperform nonmusicians on a variety of tasks. Here we provide the first evidence that musicians have superior auditory recognition memory for both musical and nonmusical stimuli, compared to nonmusicians. However, this advantage did not generalize to the visual domain. Previously, we showed that auditory recognition memory is inferior to visual recognition memory. Would this be true even for trained musicians? We compared auditory and visual memory in musicians and nonmusicians using familiar music, spoken English, and visual objects. For both groups, memory for the auditory stimuli was inferior to memory for the visual objects. Thus, although considerable musical training is associated with better musical and nonmusical auditory memory, it does not increase the ability to remember sounds to the levels found with visual stimuli. This suggests a fundamental capacity difference between auditory and visual recognition memory, with a persistent advantage for the visual domain.
… of pathology & …, Jan 1, 2011
N Context.-Medical screening tasks are often difficult, visual searches with low target prevalenc... more N Context.-Medical screening tasks are often difficult, visual searches with low target prevalence (low rates of disease). Under laboratory conditions, when targets are rare, nonexpert searchers show decreases in false-positive results and increases in false-negative results compared with results when targets are common. This prevalence effect is not due to vigilance failures or target unfamiliarity.
Attention, Perception, & …, Jan 1, 2011
In general, humans have impressive recognition memory for previously viewed pictures. Many people... more In general, humans have impressive recognition memory for previously viewed pictures. Many people spend years becoming experts in highly specialized image sets. For example, cytologists are experts at searching micrographs filled with potentially cancerous cells and radiologists are expert at searching mammograms for indications of cancer. Do these experts develop robust visual long-term memory for their domain of expertise? If so, is this expertise specific to the trained image class, or do such experts possess generally superior visual memory? We tested recognition memory of cytologists, radiologists, and controls with no medical experience for three visual stimulus classes: isolated objects, scenes, and mammograms or micrographs. Experts were better than control observers at recognizing images from their domain, but their memory for those images was not particularly good (D' ~ 1.0) and was much worse than memory for objects or scenes (D' > 2.0). Furthermore, experts were not better at recognizing scenes or isolated objects than control observers.
Journal of Vision, Jan 1, 2005
Abstract Objects and events in the environment typically produce correlated input to several sens... more Abstract Objects and events in the environment typically produce correlated input to several sensory modalities at once. It is important to understand the conditions under which the different sensory streams are integrated and the supporting mechanism. We ask whether there is crossmodal binding of non-speech auditory and visual stimuli and how and where it is realized physiologically. Do the pitch of a sound and the location of a visual object have some crossmodal correspondence that might provide a basis for their integration (as ...
Psychological science, Jan 1, 2011
Journal of …, Jan 1, 2005
The neural mechanism that mediates perceptual filling-in of the blind spot is still under discuss... more The neural mechanism that mediates perceptual filling-in of the blind spot is still under discussion. One hypothesis proposes that the cortical representation of the blind spot is activated only under conditions that elicit perceptual filling-in, and requires congruent stimulation on both sides of the blind spot. Alternatively, the passive remapping hypothesis proposes that inputs from regions surrounding the blind spot infiltrate the representation of the blind spot in cortex. This theory predicts that independent stimuli presented to the left and right of the blind spot should lead to neighboring/ overlapping activations in visual cortex when the blind-spot eye is stimulated, but separated activations when the fellow eye is stimulated. Using functional MRI, we directly tested the remapping hypothesis by presenting flickering checkerboard wedges to the left or right of the spatial location of the blind spot, either to the blind-spot eye or to the fellow eye. Irrespective of which eye was stimulated, we found separate activations corresponding to the left and right wedges. We identified the centroid of the activations on a cortical flat map and measured the distance between activations. Distance measures of the cortical gap across the blind spot were accurate and reliable (mean distance 6-8 mm across subjects, SD ~1 mm within subjects). Contrary to the predictions of the remapping hypothesis, cortical distances between activations to the two wedges were equally large for the blindspot eye and fellow eye in areas V1 and V2/V3. Remapping therefore appears unlikely to account for perceptual filling-in at an early cortical level.
Trends in cognitive sciences, Jan 1, 2011
How do we find objects in scenes? For decades, visual search models have been built on experiment... more How do we find objects in scenes? For decades, visual search models have been built on experiments in which observers search for targets, presented among distractor items, isolated and randomly arranged on blank backgrounds. Are these models relevant to search in continuous scenes? This paper argues that the mechanisms that govern artificial, laboratory search tasks do play a role in visual search in scenes. However, scene-based information is used to guide search in ways that had no place in earlier models. Search in scenes may be best explained by a dual-path model: A "selective" path in which candidate objects must be individually selected for recognition and a "non-selective" path in which information can be extracted from global / statistical information.
Journal of vision, Jan 1, 2010
The brain may combine information from different sense modalities to enhance the speed and accura... more The brain may combine information from different sense modalities to enhance the speed and accuracy of detection of objects and events, and the choice of appropriate responses. There is mounting evidence that perceptual experiences that appear to be modality-specific are also influenced by activity from other sensory modalities, even in the absence of awareness of this interaction. In a series of speeded classification tasks, we found spontaneous mappings between the auditory feature of pitch and the visual features of vertical location, size, and spatial frequency but not contrast. By dissociating the task variables from the features that were cross-modally related, we find that the interactions happen in an automatic fashion and are possibly located at the perceptual level.
…, Jan 1, 2007
In a functional magnetic resonance imaging experiment, we explored whether affective person knowl... more In a functional magnetic resonance imaging experiment, we explored whether affective person knowledge based on memories formed from minimal information is spontaneously retrieved in face perception. In the first stage of the experiment, participants were presented with 120 unfamiliar faces. Each face was presented with a description of one of four types of behaviors: aggressive, disgusting, neutral, and nice. In the second stage, participants were scanned while engaged in a one-back recognition task in which they saw the faces that were associated with behaviors and 30 novel faces. Although this task is a simple perceptual task that neither demands person evaluation nor retrieval of person knowledge, neural responses to faces differed as a function of the behaviors. Faces associated with behaviors evoked stronger activity than did novel faces in regions implicated in social cognition-anterior paracingulate cortex and superior temporal sulcus. Explicit memory for the behaviors enhanced the neural response in these regions. Faces associated with disgusting behaviors evoked stronger activity in left anterior insula than did faces associated with aggressive behaviors. This effect was equally strong for faces associated with explicitly recalled behaviors and faces associated with non-recalled behaviors. The findings suggest that affective person knowledge acquired from minimal information is spontaneously retrieved in face perception, engaging neural systems for analysis of social cognition and emotions.
Journal of Experimental Psychology: …, Jan 1, 2005
Studies have suggested attention-free semantic processing of natural scenes in which concurrent t... more Studies have suggested attention-free semantic processing of natural scenes in which concurrent tasks leave category detection unimpaired (e.g., F. Li, R. VanRullen, C. Koch, & P. . Could this ability reflect detection of disjunctive feature sets rather than high-level binding? Participants detected an animal target in a rapid serial visual presentation (RSVP) sequence and then reported its identity and location. They frequently failed to identify or to localize targets that they had correctly detected, suggesting that detection was based only on partial processing. Detection of targets was considerably worse in sequences that also contained humans, presumably because of shared features. When 2 targets were presented in RSVP, a prolonged attentional blink appeared that was almost eliminated when both targets were detected without being identified. The results suggest rapid feature analysis mediating detection, followed by attention-demanding binding for identification and localization.
Abstract Diagnostic accuracy for radiologists is above that expected by chance when they are expo... more Abstract Diagnostic accuracy for radiologists is above that expected by chance when they are exposed to a chest radiograph for only one-fifth of a second, a period too brief for more than a single voluntary eye movement. How do radiologists glean information from a first glance at an image? It is thought that this expert impression of the gestalt of an image is related to the everyday, immediate visual understanding of the gist of a scene. Several high-speed mechanisms guide our search of complex images.
Abstract A typical visual scene we encounter in everyday life is complex and filled with a huge a... more Abstract A typical visual scene we encounter in everyday life is complex and filled with a huge amount of perceptual information. The term,'visual attention'describes a set of mechanisms that limit some processing to a subset of incoming stimuli. Attentional mechanisms shape what we see and what we can act upon. They allow for concurrent selection of some (preferably, relevant) information and inhibition of other information. This selection permits the reduction of complexity and informational overload.
Abstract The ability to detect relationships between different sensory events grants behavioral f... more Abstract The ability to detect relationships between different sensory events grants behavioral flexibility, permitting the substitution of one sensory channel for another as well as the integration of information from different sensory streams. Studies in this dissertation examine the featural correspondence between basic auditory and visual features, exploring the nature, the neural correlates and the role of attention in their interaction.
Journal of Vision, Jan 1, 2010
Abstract Observers can report some semantic content of scenes when those scenes are presented for... more Abstract Observers can report some semantic content of scenes when those scenes are presented for 20 msec, flanked in time by masks. It is likely that only a single object could be selected for attentional processing in this time so this gist processing would seem to involve non-selective processing of the entire image. Similarly, we find that expert observers (radiologists and cytopathologists) can detect subtle signs of cancer at above chance levels in 250 msec exposures of mammograms and Pap-smears. These exposures are ...
Journal of Vision, Jan 1, 2004
Abstract How much is possible outside the focus of attention? Recent studies have argued that per... more Abstract How much is possible outside the focus of attention? Recent studies have argued that perception of natural scenes contradicts common findings of limited capacity of visual attention. They have shown that participants detect a natural category target in real scenes, just as well in a dual task situation as when the scene receives full attention (Li et al. 2002). Furthermore they are able to search two scenes in parallel in a go-no-go natural category detection task (Rousselet et al. 2002). We believe that this ability may not be due to high- ...
Journal of Vision, Jan 1, 2006
Abstract The brain derives information from several sense modalities to enhance the speed and acc... more Abstract The brain derives information from several sense modalities to enhance the speed and accuracy of detection of objects and events, and the choice of appropriate responses. There is mounting evidence that perceptual experiences that may appear to be modality specific are also influenced by activity from other sensory modalities, even in the absence of awareness of this interaction. In a series of speeded classification tasks we found natural spontaneous mappings between the pitch of sounds and the visual features of vertical ...
Journal of Vision, Jan 1, 2009
Abstract It has been well documented that people are able to get some semantic and/or statistical... more Abstract It has been well documented that people are able to get some semantic and/or statistical information out of a briefly presented image. They are able to report on the gist of a scene in 100 ms (Potter, 1975), detect the presence of an animal in an image presented for 20 ms (Thorpe et al., 1996) and determine the mean size of sets of objects (Ariely, 2001; Chong & Treisman, 2003). These findings suggest that some advanced scene processing is possible without attentional selection of specific objects. What are the limits on this non- ...
Wiley Interdisciplinary Reviews: …, Jan 1, 2011
Quantity or numerosity is one of the basic properties of our environment. Humans and animals both... more Quantity or numerosity is one of the basic properties of our environment. Humans and animals both have the neural representation of quantity or "number sense". The ability to extract and to manipulate numbers is closely related to our various cognitive functions such as the capacity of working memory, mathematical achievement, and texture perception. Evidence shows that the sense of number is not a unitary mechanism but rather a composition of two distinct processes; enumeration and estimation. The review examines how numerosity is represented in the visual domain and its relation to different modes of attention. Enumeration or counting permits an exact representation of a distinct number of objects, with an awareness of each object achieved through focal deployment of attention to each object serially. On the other hand, estimation involves an approximation of the number of different items or a sense of ensemble statistics, achieved through fast deployment of distributed attention over a set of objects as a whole. In this overview we suggest that a focused attention mode is more suitable for enumeration, whereas a distributed attention mode is better for estimation.
Psychonomic bulletin & …, Jan 1, 2011
Numerous studies have shown that musicians outperform nonmusicians on a variety of tasks. Here we... more Numerous studies have shown that musicians outperform nonmusicians on a variety of tasks. Here we provide the first evidence that musicians have superior auditory recognition memory for both musical and nonmusical stimuli, compared to nonmusicians. However, this advantage did not generalize to the visual domain. Previously, we showed that auditory recognition memory is inferior to visual recognition memory. Would this be true even for trained musicians? We compared auditory and visual memory in musicians and nonmusicians using familiar music, spoken English, and visual objects. For both groups, memory for the auditory stimuli was inferior to memory for the visual objects. Thus, although considerable musical training is associated with better musical and nonmusical auditory memory, it does not increase the ability to remember sounds to the levels found with visual stimuli. This suggests a fundamental capacity difference between auditory and visual recognition memory, with a persistent advantage for the visual domain.
… of pathology & …, Jan 1, 2011
N Context.-Medical screening tasks are often difficult, visual searches with low target prevalenc... more N Context.-Medical screening tasks are often difficult, visual searches with low target prevalence (low rates of disease). Under laboratory conditions, when targets are rare, nonexpert searchers show decreases in false-positive results and increases in false-negative results compared with results when targets are common. This prevalence effect is not due to vigilance failures or target unfamiliarity.
Attention, Perception, & …, Jan 1, 2011
In general, humans have impressive recognition memory for previously viewed pictures. Many people... more In general, humans have impressive recognition memory for previously viewed pictures. Many people spend years becoming experts in highly specialized image sets. For example, cytologists are experts at searching micrographs filled with potentially cancerous cells and radiologists are expert at searching mammograms for indications of cancer. Do these experts develop robust visual long-term memory for their domain of expertise? If so, is this expertise specific to the trained image class, or do such experts possess generally superior visual memory? We tested recognition memory of cytologists, radiologists, and controls with no medical experience for three visual stimulus classes: isolated objects, scenes, and mammograms or micrographs. Experts were better than control observers at recognizing images from their domain, but their memory for those images was not particularly good (D' ~ 1.0) and was much worse than memory for objects or scenes (D' > 2.0). Furthermore, experts were not better at recognizing scenes or isolated objects than control observers.
Journal of Vision, Jan 1, 2005
Abstract Objects and events in the environment typically produce correlated input to several sens... more Abstract Objects and events in the environment typically produce correlated input to several sensory modalities at once. It is important to understand the conditions under which the different sensory streams are integrated and the supporting mechanism. We ask whether there is crossmodal binding of non-speech auditory and visual stimuli and how and where it is realized physiologically. Do the pitch of a sound and the location of a visual object have some crossmodal correspondence that might provide a basis for their integration (as ...
Psychological science, Jan 1, 2011
Journal of …, Jan 1, 2005
The neural mechanism that mediates perceptual filling-in of the blind spot is still under discuss... more The neural mechanism that mediates perceptual filling-in of the blind spot is still under discussion. One hypothesis proposes that the cortical representation of the blind spot is activated only under conditions that elicit perceptual filling-in, and requires congruent stimulation on both sides of the blind spot. Alternatively, the passive remapping hypothesis proposes that inputs from regions surrounding the blind spot infiltrate the representation of the blind spot in cortex. This theory predicts that independent stimuli presented to the left and right of the blind spot should lead to neighboring/ overlapping activations in visual cortex when the blind-spot eye is stimulated, but separated activations when the fellow eye is stimulated. Using functional MRI, we directly tested the remapping hypothesis by presenting flickering checkerboard wedges to the left or right of the spatial location of the blind spot, either to the blind-spot eye or to the fellow eye. Irrespective of which eye was stimulated, we found separate activations corresponding to the left and right wedges. We identified the centroid of the activations on a cortical flat map and measured the distance between activations. Distance measures of the cortical gap across the blind spot were accurate and reliable (mean distance 6-8 mm across subjects, SD ~1 mm within subjects). Contrary to the predictions of the remapping hypothesis, cortical distances between activations to the two wedges were equally large for the blindspot eye and fellow eye in areas V1 and V2/V3. Remapping therefore appears unlikely to account for perceptual filling-in at an early cortical level.
Trends in cognitive sciences, Jan 1, 2011
How do we find objects in scenes? For decades, visual search models have been built on experiment... more How do we find objects in scenes? For decades, visual search models have been built on experiments in which observers search for targets, presented among distractor items, isolated and randomly arranged on blank backgrounds. Are these models relevant to search in continuous scenes? This paper argues that the mechanisms that govern artificial, laboratory search tasks do play a role in visual search in scenes. However, scene-based information is used to guide search in ways that had no place in earlier models. Search in scenes may be best explained by a dual-path model: A "selective" path in which candidate objects must be individually selected for recognition and a "non-selective" path in which information can be extracted from global / statistical information.
Journal of vision, Jan 1, 2010
The brain may combine information from different sense modalities to enhance the speed and accura... more The brain may combine information from different sense modalities to enhance the speed and accuracy of detection of objects and events, and the choice of appropriate responses. There is mounting evidence that perceptual experiences that appear to be modality-specific are also influenced by activity from other sensory modalities, even in the absence of awareness of this interaction. In a series of speeded classification tasks, we found spontaneous mappings between the auditory feature of pitch and the visual features of vertical location, size, and spatial frequency but not contrast. By dissociating the task variables from the features that were cross-modally related, we find that the interactions happen in an automatic fashion and are possibly located at the perceptual level.
…, Jan 1, 2007
In a functional magnetic resonance imaging experiment, we explored whether affective person knowl... more In a functional magnetic resonance imaging experiment, we explored whether affective person knowledge based on memories formed from minimal information is spontaneously retrieved in face perception. In the first stage of the experiment, participants were presented with 120 unfamiliar faces. Each face was presented with a description of one of four types of behaviors: aggressive, disgusting, neutral, and nice. In the second stage, participants were scanned while engaged in a one-back recognition task in which they saw the faces that were associated with behaviors and 30 novel faces. Although this task is a simple perceptual task that neither demands person evaluation nor retrieval of person knowledge, neural responses to faces differed as a function of the behaviors. Faces associated with behaviors evoked stronger activity than did novel faces in regions implicated in social cognition-anterior paracingulate cortex and superior temporal sulcus. Explicit memory for the behaviors enhanced the neural response in these regions. Faces associated with disgusting behaviors evoked stronger activity in left anterior insula than did faces associated with aggressive behaviors. This effect was equally strong for faces associated with explicitly recalled behaviors and faces associated with non-recalled behaviors. The findings suggest that affective person knowledge acquired from minimal information is spontaneously retrieved in face perception, engaging neural systems for analysis of social cognition and emotions.
Journal of Experimental Psychology: …, Jan 1, 2005
Studies have suggested attention-free semantic processing of natural scenes in which concurrent t... more Studies have suggested attention-free semantic processing of natural scenes in which concurrent tasks leave category detection unimpaired (e.g., F. Li, R. VanRullen, C. Koch, & P. . Could this ability reflect detection of disjunctive feature sets rather than high-level binding? Participants detected an animal target in a rapid serial visual presentation (RSVP) sequence and then reported its identity and location. They frequently failed to identify or to localize targets that they had correctly detected, suggesting that detection was based only on partial processing. Detection of targets was considerably worse in sequences that also contained humans, presumably because of shared features. When 2 targets were presented in RSVP, a prolonged attentional blink appeared that was almost eliminated when both targets were detected without being identified. The results suggest rapid feature analysis mediating detection, followed by attention-demanding binding for identification and localization.