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Biomedical subjects

P A McMullen

Publications and source records attributed to P A McMullen.

10 recordsLinked to original sources
PubMed2002

Changes to the object recognition system in patients with dementia of the Alzheimer's type.

Do DAT patients show category-specific deficits in object identification, and do they arise from semantic or visual damage? Participants decided whether line drawings of living and nonliving objects matched names at superordinate, basic, or subordinate levels. Patients were most impaired with superordinate decisions. Controls had most difficulty with subordinate decisions. No category-specific deficit was found with patients. Impaired superordinate decisions by the patients support semantic damage. If category-specific deficits arise from damaged semantics, they should have been found. Since they were not, and since patients performed subordinate decisions the best, a visual basis to category specificity is supported. Finally, a living advantage was found with normal observers which cannot be spurious due to differences in concept familiarity since living and nonliving objects were matched for this variable.

Adolescent↗
PubMed2000

Testing a two-component model of face identification: effects of inversion, contrast reversal, and direction of lighting.

Enns and Shore (1997 Perception & Psychophysics 59 23-31) found additive effects of test orientation (upright or inverted) and direction of lighting (brow or chin lit) when they studied the inversion effect on face identification. A two-stage model was inferred in which inversion was processed by an orientation-sensitive component after which chin-lighting was processed by a lighting-sensitive component. Face identification is also strongly influenced by contrast reversal. A study is reported which aimed to (i) determine if contrast reversal interacts with lighting direction or orientation, findings that would support Enns and Shore's model; and (ii) to test their assumption that holistic encoding is prerequisite for their model by inducing featural encoding through training names to inverted faces. Names for unfamiliar brow-lit positive-contrast faces were trained with the faces upright or inverted. Identification accuracy was measured with combinations of orientation, lighting, and contrast. Consistent with their model, test orientation and direction of lighting were additive after training on upright faces and lighting and contrast reversal interacted. When holistic encoding was prevented following training on inverted faces, test orientation and lighting direction interacted for positive-contrast faces. Negative faces showed only an effect of direction of lighting. These results support Enns and Shore's two-stage model and their interpretation that orientation and direction of lighting interact following featural encoding of faces.

Analysis of Variance↗
PubMed1998

Effects of orientation on the identification of rotated objects depend on the level of identity.

Matching names and rotated line drawings of objects showed effects of object orientation that depended on name level. Large effects, in the same range as object naming, were found for rotations between 0 degrees and 120 degrees from upright with subordinate names (e.g., collie), whereas nonsignificant effects were found with superordinate (e.g., animal) and basic names (e.g., dog). These results support image normalization, after contact with orientation-invariant representations, that provide basic-level identity. They consequently fail to support theories of object recognition in which rotated object images are normalized to the upright position before contact with long-term object representations.

Adolescent↗
PubMed1995

Rotated object identification with and without orientation cues.

The time to name two-dimensional line drawings of objects increases linearly for object rotations between 0 degrees and 120 degrees from the upright. Several theories attribute these effects of orientation to finding the top or the top-bottom axis of objects. By this account, prior knowledge of the location of the top or the top-bottom axis of objects should diminish effects of object orientation when they are named. When this hypothesis was tested by cuing the top or the top-bottom axis, no reduction in the effects of orientation on object naming was found. This result is inconsistent with effects of orientation on object naming being due to finding the top or the top-bottom axis. Instead, the top may be found prior to rotational normalization of the object image.

Humans↗
PubMed1993

Orientation-invariant transfer of training in the identification of rotated natural objects.

The effects of stimulus orientation on naming were examined in two experiments in which subjects identified line drawings of natural objects following practice with the objects at the same or different orientations. Half the rotated objects were viewed in the orientation that matched the earlier presentations, and half were viewed at an orientation that mismatched the earlier presentations. Systematic effects of orientation on naming time were found during the early presentations. These effects were reduced during later presentations, and the size of this reduction did not depend on the orientation in which the object had been seen originally. The results are consistent with a dual-systems model of object identification in which initially large effects of disorientation are the result of a normalization process such as mental rotation, and in which attenuation of the effects is due to a shift from the normalization system to a feature/part-based system.

Adult↗
PubMed1992

Reference frame and effects of orientation on finding the tops of rotated objects.

Effects of stimulus orientation across trial blocks and the spatial reference frame were investigated with a task in which Ss, with their head upright or tilted, judged a dot to be near the top or the bottom of rotated line drawings of objects. Objects used in this task were also named. Response times from the first block of trials increased linearly for objects rotated from 0 degrees to 120 degrees from the upright. Across blocks, orientation effects diminished for naming but remained the same for top-bottom discriminations. Practice with top-bottom discriminations diminished orientation effects when the same objects were subsequently named. The spatial reference frame for top-bottom discriminations was midway between retinal and environmental coordinates. Specifying the location of object features is of greater importance for top-bottom discriminations than for naming and underlies orientation effects in these tasks.

Adult↗
PubMed1991

Can recognition of living things be selectively impaired?

Brain damage sometimes seems to impair recognition of living things, despite relatively preserved recognition of nonliving things. The most straightforward interpretation of this dissociation is that the recognition of living things depends on some specialized mechanisms that are not needed for the recognition of nonliving things. However, there are alternative interpretations of the dissociation in terms of the greater complexity or inter-item similarity of living things, or the more specific, within-category identifications that are usually required for living things. Surprisingly, the relevant tests to discriminate among these rival hypotheses have never been performed. We took the factors of visual complexity, inter-item similarity, specificity of identification, as well as others, into account in analyzing the visual recognition performance of two head-injured visual agnosic patients. In each case we found that recognition of living things was still disproportionately impaired when the effects of the other factors were accounted for.

Adult↗
PubMed1990

The spatial frame of reference in object naming and discrimination of left-right reflections.

The effects of stimulus rotation and observer's head-tilt position on various pattern-recognition tasks were investigated to compare the external directions most closely aligned with the spatial frame of reference. Specifically, the effects of these factors on the time to name objects were compared with their effects on the time to discriminate left-facing from right-facing lateral views of these objects, as well as with their effects on the time to discriminate normal from mirror-imaged alphanumeric characters. The naming task relied upon a reference frame more closely aligned with retinal directions than with environmental directions. In contrast, both discrimination tasks relied upon a frame aligned more closely with environmental directions. Overall, the nature of the task exerts a greater influence on the directions with which the frame of reference is aligned than do the stimulus attributes.

Adult↗
PubMed1984

Morphological alterations in rat CA1 hippocampal pyramidal cell dendrites resulting from chronic ethanol consumption and withdrawal.

Hippocampal CA1 pyramidal cell dendrites were studied in rats after 5 months of consumption of an ethanol liquid diet and 5 months of ethanol diet followed by 2 months of withdrawal. Morphometric data were compared with those obtained from matched littermate, yoke -fed control animals. Dendritic branching in Golgi-Cox-stained tissues was assessed by standard and modified Sholl analysis techniques and basilar dendrites were analysed three-dimensionally by computer. Five months of chronic ethanol consumption caused a significant decrease in the number of second-order basilar dendrites, 60-90 micron from the apical border of the cell layer. No significant changes in the neuronal density of CA1 or CA3 cells were found; however, the thickness of the strata oriens and radiatum of the CA1 field was significantly decreased in the ethanol-fed group. After 5 months of chronic ethanol consumption and 2 months of withdrawal, the thickness of the strata returned to control sizes and the frequency of proximal basilar branching recovered. Evidence of lengthening and new branching of distal basilar dendrites occurred in the third-, fourth-, and fifth-order segments when control animals 6 and 8 months of age were compared. During the 2-month period of withdrawal, the number and length of third-, fourth-, and fifth-order segments of basilar dendrites increased when compared to the nonwithdrawn ethanol group while the number and length of second- and third-order segments decreased. This is comparable to the changes seen during normal aging and suggests that withdrawal may interact with aging to produce enhanced dendritic growth in "compensation" for the developmental retardation induced by chronic ethanol intake.

Alcohol Withdrawal Delirium↗