Biomedical subjects

Jennifer K E Steeves

Publications and source records attributed to Jennifer K E Steeves.

5 recordsLinked to original sources

PubMed2005

The fusiform face area is not sufficient for face recognition: evidence from a patient with dense prosopagnosia and no occipital face area.

We tested functional activation for faces in patient D.F., who following acquired brain damage has a profound deficit in object recognition based on form (visual form agnosia) and also prosopagnosia that is undocumented to date. Functional imaging demonstrated that like our control observers, D.F. shows significantly more activation when passively viewing face compared to scene images in an area that is consistent with the fusiform face area (FFA) (p < 0.01). Control observers also show occipital face area (OFA) activation; however, whereas D.F.'s lesions appear to overlap the OFA bilaterally. We asked, given that D.F. shows FFA activation for faces, to what extent is she able to recognize faces? D.F. demonstrated a severe impairment in higher level face processing--she could not recognize face identity, gender or emotional expression. In contrast, she performed relatively normally on many face categorization tasks. D.F. can differentiate faces from non-faces given sufficient texture information and processing time, and she can do this is independent of color and illumination information. D.F. can use configural information for categorizing faces when they are presented in an upright but not a sideways orientation and given that she also cannot discriminate half-faces she may rely on a spatially symmetric feature arrangement. Faces appear to be a unique category, which she can classify even when she has no advance knowledge that she will be shown face images. Together, these imaging and behavioral data support the importance of the integrity of a complex network of regions for face identification, including more than just the FFA--in particular the OFA, a region believed to be associated with low-level processing.

Adolescent↗

PubMed2004

Global shape discrimination at reduced contrast in enucleated observers.

Previous research has shown that observers with early unilateral enucleation have selectively better sensitivity to luminance contrast than monocular viewing controls [González et al., 2002; Vision Research 36 (1) (1996) 175; Vision Research 36 (1996) 3011; Vision Research 37 (17) (1997) 2465]. We asked whether unilateral enucleation specifically enhances all levels of luminance processing. Enucleated observers, as well as binocular and monocular viewing controls, detected global shape in radial frequency (RF) patterns [Vision Research 38 (1998) 2555] at low contrast. Control observers were tested in two monocular conditions in which the stimulus was presented to one eye, while the fellow eye: (1) viewed a luminance-matched grey field or (2) was covered by a dark eye patch. Sensitivity to low-contrast global shape was equivalent in enucleated observers and binocular controls. More importantly, enucleated observers showed superior performance to that of controls in either monocular condition. At low contrast, the dichoptic control group was more sensitive than controls wearing an eye patch, which suggests that dichoptic viewing is a superior method of testing when comparing monocular control performance to that of monocularly deprived populations. The previously reported enhanced sensitivity to luminance-defined form in early enucleated observers also occurs for low-contrast global shape discrimination.

Adolescent↗

PubMed2002

Foveal and eccentric acuity in one-eyed observers.

The purpose of these two experiments was to examine the effects of enucleation on the foveal and near-periphery acuity of human observers. In Experiment 1, using high contrast illiterate-E optotypes, we measured foveal and 7-degree eccentric (nasal and temporal) acuity in the remaining eye of unilaterally enucleated children and adults. The data were compared to those of the fellow or 'good eye' of age-matched non-amblyopic and amblyopic strabismic observers-a different kind of monocular deprivation-and binocularly normal subjects. The main finding was that the 7-degree eccentric acuity of enucleated observers and normal controls was best, followed by that of the non-amblyopic and lastly, the amblyopic subjects. There were no naso-temporal asymmetries. In Experiment 2, foveal and 7-degree eccentric acuities of enucleated and binocularly normal subjects were tested at 96, 13.5 and 4.7% contrast levels using the same kind of stimuli. The foveal acuity of the enucleated observers was better than the monocular acuity of controls at all contrasts, and equivalent to their binocular acuity. The eccentric acuity of the enucleated observers was better at the two low contrast levels. No naso-temporal asymmetries were found in either group at any contrast level. These findings suggest that, in humans, visual deprivation from unilateral enucleation does not result in a naso-temporal asymmetry in the near periphery.

Adolescent↗

PubMed2002

Early unilateral enucleation disrupts motion processing.

Previous research has shown that unilaterally enucleated observers demonstrate better luminance-defined form perception compared to monocularly viewing controls, and similar performance to control observers viewing binocularly (Vision Res. 37(17) (1997) 2465). In Experiment 1 we asked whether the perception of form, where form is defined by other attributes than luminance, is also improved compared to monocularly viewing controls. We tested 16 enucleated observers and 25 controls viewing monocularly and binocularly for their ability to detect and recognize form from texture (texture-defined (TD) form) and form from motion (motion-defined (MD) form). There was no difference between the three groups for TD form perception. However, enucleated observers had significantly poorer MD form perception than did binocularly viewing controls. In Experiment 2 we asked whether poor performance on the perception of MD form might be due to a general reduction in motion processing abilities. To examine this possibility, we used a motion coherence task. We tested eight unilaterally enucleated and 14 monocularly and binocularly viewing control observers on a horizontal coherent motion discrimination task. The monocularly viewing controls showed no naso-temporal asymmetry in direction discrimination for coherent motion. In contrast, the enucleated group showed an asymmetry in direction discrimination where temporalward motion coherence thresholds were significantly higher than those for nasalward motion. These latter findings are discussed in terms of the absence of binocular competition during the development of motion processing pathways.

Adolescent↗

PubMedDate not supplied

Behavioral and neuroimaging evidence for a contribution of color and texture information to scene classification in a patient with visual form agnosia.

A common notion is that object perception is a necessary precursor to scene perception. Behavioral evidence suggests, however, that scene perception can operate independently of object perception. Further, neuroimaging has revealed a specialized human cortical area for viewing scenes that is anatomically distinct from areas activated by viewing objects. Here we show that an individual with visual form agnosia, D.F., who has a profound deficit in object recognition but spared color and visual texture perception, could still classify scenes and that she was fastest when the scenes were presented in the appropriate color. When scenes were presented as black-and-white images, she made a large number of errors in classification. Functional magnetic resonance imaging revealed selective activation in the parahippocampal place area (PPA) when D.F. viewed scenes. Unlike control observers, D.F. demonstrated higher activation in the PPA for scenes presented in the appropriate color than for black-and-white versions. The results demonstrate that an individual with profound form vision deficits can still use visual texture and color to classify scenes-and that this intact ability is reflected in differential activation of the PPA with colored versions of scenes.

Adult↗