H M Buchanan-Smith

Publications of H M Buchanan-Smith

• The impact of moving to a novel environment on social networks, activity and wellbeing in two new world primates.

  Authors: V Dufour, C Sueur, A Whiten, H M Buchanan-Smith

  American journal of primatology. 03/2011; 73(8):802-11.

  Among the stressors that can affect animal welfare in zoos, the immediate effect of relocation to a novel environment is one that has received little attention in the literature. Here, we compare theAmong the stressors that can affect animal welfare in zoos, the immediate effect of relocation to a novel environment is one that has received little attention in the literature. Here, we compare the social network, daily activity and the expression of stress-related behavior in capuchins (Cebus apella) and squirrel monkeys (Saimiri sciureus) before and just after they were relocated to a new enriched enclosure. Results showed similar immediate responses to the move in the two species. Both showed a substantial increase in the time spent resting and spent more time in the highest and "safest" part of their enclosure after relocation. Both capuchins and squirrel monkeys spent significantly more time in close proximity to other group members after relocation, compared to before. In squirrel monkeys, the structure of the social network, which was initially correlated to affiliation, was no longer so after the move. In capuchins, the network analysis showed that individuals regrouped by age, with the youngsters who were potentially more affected by stress being in the center of the network. Social network analysis helped to achieve a more complete picture of how individuals were affected by relocation. We suggest that this type of analysis should be used alongside traditional methods of observation and analysis to encompass the most complex aspects of animal behavior in times of stress and to improve welfare.

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• Animal behaviour. An unusual social display by gorillas.

  Authors: R J Parnell, H M Buchanan-Smith

  Nature. 08/2001; 412(6844):294.

• The behavioural ecology of mixed-species troops of callitrichine primates.

  Authors: E W Heymann, H M Buchanan-Smith

  Biological reviews of the Cambridge Philosophical Society. 06/2000; 75(2):169-90.

  This review summarizes information on the behavioural ecology of mixed-species troops (interspecific associations) formed by different species of callitrichines, small New World monkeys, in westernThis review summarizes information on the behavioural ecology of mixed-species troops (interspecific associations) formed by different species of callitrichines, small New World monkeys, in western and central Amazonia. The formation of mixed-species troops is an integral part of the biology of several species of this subfamily. Niche separation between associated species is obtained through vertical segregation which results in differences in the prey spectrum. The degree of niche separation is a predictor for the stability of mixed-species troops. Individuals may benefit from the formation of mixed-species troops through increased safety from predators, increased foraging efficiency, and/or increased resource defence. Costs of mixed-species troop formation are probably very low and mainly relate to patterns of interspecific behavioural interactions. We point to gaps in our knowledge and suggest pathways for future research into mixed-species troops.

• The influence of stimulus shape on orientation acuity.

  Authors: D W Heeley, H M Buchanan-Smith

  Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale. 06/1998; 120(2):217-22.

  Orientation acuity was estimated for vertical and oblique bar stimuli. Discrimination thresholds were affected by changes in the length and width of the targets, falling as bar length was increasedOrientation acuity was estimated for vertical and oblique bar stimuli. Discrimination thresholds were affected by changes in the length and width of the targets, falling as bar length was increased and, conversely, rising as the bars were made wider. These changes are complimentary, in that overall discrimination performance can be predicted by a single measure of the orientation "entropy" of the target, namely the height-to-width ratio. The data provide support for a model of orientation coding where discrimination performance is not simply a reflection of the signal-to-noise ratio in single cells in the striate cortex.

• The oblique effect in orientation acuity.

  Authors: D W Heeley, H M Buchanan-Smith, J A Cromwell, J S Wright

  Vision research. 02/1997; 37(2):235-42.

  We have examined the dependence of rotational acuity on the orientation bandwidth of a stimulus using two-dimensional, band-pass filtered, spatial noise. Stimuli had a bandwidth of 0.5 octave ofWe have examined the dependence of rotational acuity on the orientation bandwidth of a stimulus using two-dimensional, band-pass filtered, spatial noise. Stimuli had a bandwidth of 0.5 octave of spatial frequency, centred at 5.0 cyc/deg, and an orientation bandwidth that covered the range from 0.0 to 25.0 deg. Thresholds were obtained on one principal (vertical), and one oblique axis (45 deg). It was found that acuity declined on both axes as bandwidth increased, in a manner that was compatible with simple statistical principles with virtually perfect sampling of the image. There was some evidence that the intrinsic noise is greater on the oblique axis than on the vertical, and that oblique axes are less densely sampled than the principal axes. These differences are small and are insufficient, either on their own or taken together to explain the oblique effect.

• Mechanisms specialized for the perception of image geometry.

  Authors: D W Heeley, H M Buchanan-Smith

  Vision research. 12/1996; 36(22):3607-27.

  Angle discrimination thresholds were obtained for V-shaped targets with a base angle of 90 deg at four different pattern orientations (0, 45, 90 and 135 deg). A comparison of these thresholds withAngle discrimination thresholds were obtained for V-shaped targets with a base angle of 90 deg at four different pattern orientations (0, 45, 90 and 135 deg). A comparison of these thresholds with the orientation discrimination thresholds for the single lines from which the patterns had been constructed, revealed that angle acuity cannot be predicted from component acuity. Angle acuity is finer than the corresponding orientation acuity in all cases and does not exhibit the pronounced oblique effect that is found for orientation discrimination. Other experiments showed that acuity for pattern angle depends critically on base angle, with minima close to 0, 90 and 180 deg. The shape and amplitude of this function are independent of pattern orientation. It was found that the angle acuity was unaffected by excluding a large portion of the target in the region of the vertex, and that the pattern of dependence of acuity on angle changed radically when the target was reduced ultimately to three blobs that defined the cardinal points of the stimulus. The data suggest that when the target comprises line segments, angle discrimination is not limited by noise that arises at early levels of processing and that angle perception is mediated by mechanisms that are specialized for the perception of image geometry. An opponent process model, that is based on the combined outputs of just two types of filter, is proposed as the basis for the perception of image geometry. This type of system is appropriate for computing one of the differential invariants in an optic flow field.

• Evidence for separate, task dependent noise processes in orientation and size perception.

  Authors: D W Heeley, H M Buchanan-Smith

  Vision research. 09/1994; 34(16):2059-69.

  Spatial acuity was estimated as the minimum difference in target spatial frequency which could act as a cue in a double concurrent, single interval orientation discrimination task. Experiments wereSpatial acuity was estimated as the minimum difference in target spatial frequency which could act as a cue in a double concurrent, single interval orientation discrimination task. Experiments were conducted with vertical and oblique (45 deg) targets at three different spatial frequencies covering a range of two octaves. Frequency thresholds were found to be lower than those estimated by conventional methods by a factor of nearly 50%. They followed Weber's law for target frequency and were independent of target orientation. The orientation thresholds exhibited a normal oblique effect, and were not affected by the simultaneous judgements of target frequency. The data support the contention that the neural codes for image size and image orientation are segregated at an early stage of processing, and that the main source of noise that limits the precision of coding in these domains exists beyond the level of early mechanisms.

• Changes in the perceived direction of drifting plaids, induced by asymmetrical changes in the spatio-temporal structure of the underlying components.

  Authors: D W Heeley, H M Buchanan-Smith

  Vision research. 04/1994; 34(6):775-97.

  When a plaid pattern with symmetrical velocity components (Type I) is changed to a plaid pattern with asymmetrical velocity components (Type IA), the overall direction of drift appears to undergo aWhen a plaid pattern with symmetrical velocity components (Type I) is changed to a plaid pattern with asymmetrical velocity components (Type IA), the overall direction of drift appears to undergo a rotation without any other change to the spatial parameters of the components. This change in the perceived drift direction can be induced by altering either the temporal frequency of the components or by altering their spatial frequency. In separate experiments, we have estimated the magnitude of the temporal and spatial frequency thresholds that are necessary to create a liminal change in direction of this type. The results from both temporal and spatial frequency experiments are closely similar. We find that liminal rotations can be induced by changes in the spatio-temporal structure of the sine-wave grating components that are undetectable when these components are presented in isolation. Further, we find that the "velocity threshold for direction" is not a constant factor, but critically depends on the relative orientation of the two elements that form the plaid. Forced-choice experiments were also conducted to estimate the extent of the apparent rotation of the plaid pattern for differing levels of asymmetry in the spatial frequency and temporal frequency of the components. The magnitude of the pattern rotation is predicted by a model of motion direction that encodes the successive displacements of the intersections of the gratings. Finally, we demonstrate that the velocity thresholds for perceived rotation exhibit a meridional anisotropy that depends on the direction of drift of the overall pattern and not on the orientation of the components.(ABSTRACT TRUNCATED AT 250 WORDS)

• Orientation acuity for sine-wave gratings with random variation of spatial frequency.

  Authors: D W Heeley, H M Buchanan-Smith, S Heywood

  Vision research. 01/1994; 33(17):2509-13.

  Orientation discrimination thresholds were estimated for sine-wave grating stimuli using a two-alternative forced-choice procedure on the two principal, and the two main oblique axes. The twoOrientation discrimination thresholds were estimated for sine-wave grating stimuli using a two-alternative forced-choice procedure on the two principal, and the two main oblique axes. The two discriminanda within any trial were subject to independent random variation of their spatial frequency. The variation of spatial frequency was defined by a Gaussian probability density function. Thresholds were obtained for five different depths of frequency variation within the range 0.0-1.0 octave. We find that orientation acuity on any of the axes tested is unaffected by variation in the spatial frequency of the targets. The data support the hypothesis that orientation and spatial frequency are independent and orthogonal neural codes.

• Anisotropic axes in orientation perception are not retinotopically mapped.

  Authors: H M Buchanan-Smith, D W Heeley

  Perception. 02/1993; 22(12):1389-402.

  The effect of the posture of an observer on the pattern of meridional anisotropy for orientation acuity was examined. Orientation acuity was estimated for the two principal and for one oblique axisThe effect of the posture of an observer on the pattern of meridional anisotropy for orientation acuity was examined. Orientation acuity was estimated for the two principal and for one oblique axis with three bodily postures: normal vertical sitting, vertical sitting with the head rotated to 45 degrees from vertical, and prone. The test stimuli were sine-wave gratings covering a range of two octaves of spatial frequency, thin lines, and step edges. Acuity estimates were obtained by two different psychophysical procedures: a single-interval two-alternative forced choice, and a two-interval two-alternative forced choice. Both experimental procedures revealed a strong interaction between the shape of the function that describes the meridional variation of orientation acuity and the posture of the observer. The data are incompatible with models of the oblique effect in orientation perception that are based on a meridional anisotropy in neural properties early in the visual hierarchy.

• Orientation acuity estimated with simultaneous and successive procedures.

  Authors: D W Heeley, H M Buchanan-Smith

  Spatial vision. 02/1992; 6(1):1-10.

  Orientation discrimination thresholds for medium contrast sinewave grating stimuli were estimated by a forced-choice procedure for the two principal, and the two main oblique axes. The resultsOrientation discrimination thresholds for medium contrast sinewave grating stimuli were estimated by a forced-choice procedure for the two principal, and the two main oblique axes. The results obtained for simultaneous presentation with a centre/surround stimulus arrangement are compared with the threshold estimates obtained when the two stimuli to be discriminated do not overlap in time. We find that orientation acuity depends on the temporal relationship of the discriminanda. Estimates of orientation threshold with simultaneous presentation are lower on all axes tested than those obtained with successive presentation; the greatest difference in orientation acuity was found at obliques. The data support the hypothesis that the meridional anisotropy in orientation discrimination that is found with conventional, two-interval forced-choice methods is not entirely attributable to anatomical and physiological changes at the level of the striate cortex.

• Directional acuity for drifting plaids.

  Authors: D W Heeley, H M Buchanan-Smith

  Vision research. 02/1992; 32(1):97-104.

  Orientation discrimination thresholds were estimated for symmetrical "plaids", constructed by the super-imposition of two, independent drifting sine-wave gratings of 2.5 c/deg. Experiments wereOrientation discrimination thresholds were estimated for symmetrical "plaids", constructed by the super-imposition of two, independent drifting sine-wave gratings of 2.5 c/deg. Experiments were conducted when the apparent direction of drift was on the two principal meridians (vertical and horizontal), and when the apparent direction of drift was at the two oblique orientations (45 and 135 deg). Acuity for the direction of drift for these stimuli is of the same order of precision as orientation acuity for static or drifting gratings, and exhibits a meridional anisotropy that favours the principal meridians. This anisotropy follows a pattern that is determined by the apparent direction of drift, and not the orientation of the underlying elements. Acuity for orientation is lowest for oblique drift directions, even though both of the elements are oriented on the principal meridians. This finding was confirmed when the orientation of the underlying elements was subject to a random variation. The results are not easily accommodated by models that propose that the individual elements of the plaid are analysed separately. Second, the data are incompatible with models of the oblique effect of orientation discrimination that are based on an axis dependent, differential sampling of the retinal image.

• Recognition of stimulus orientation.

  Authors: D W Heeley, H M Buchanan-Smith

  Vision research. 02/1990; 30(10):1429-37.

  The threshold for detecting a deviation in the orientation of a test stimulus from vertical and from horizontal was measured with a single test interval. The test stimuli were step edges, thin lines,The threshold for detecting a deviation in the orientation of a test stimulus from vertical and from horizontal was measured with a single test interval. The test stimuli were step edges, thin lines, and sine wave gratings of 2.5, 5.0 and 10.0 c/deg. Recognition thresholds were found to be independent of the frequency content and nature of the test stimulus. The average threshold value on the principal meridians was found to be approx. 0.6 deg. Additional testing was conducted with two interval forced choice designs, both with and without random perturbation of the orientation of the stimuli. Random perturbation of orientation reduces acuity estimates. The results are compared with those obtained by testing on the oblique meridia. We conclude that the meridional anisotropy of orientation discrimination, which favours the vertical and horizontal is a result, in part, of the influence of non-visual mechanisms.

• Mechanisms Specialized for the Perception of Image Geometry

  Authors: D.W. HEELEY, H.M. BUCHANAN-SMITH

  Vision Research.

  Angle discrimination thresholds were obtained for V-shaped targets with a base angle of 90 deg at four different pattern orientations (0, 45, 90 and 135 deg). A comparison of these thresholds withAngle discrimination thresholds were obtained for V-shaped targets with a base angle of 90 deg at four different pattern orientations (0, 45, 90 and 135 deg). A comparison of these thresholds with the orientation discrimination thresholds for the single lines from which the patterns had been constructed, revealed that angle acuity cannot be predicted from component acuity. Angle acuity is finer than the corresponding orientation acuity in all cases and does not exhibit the pronounced oblique effect that is found for orientation discrimination. Other experiments showed that acuity for pattern angle depends critically on base angle, with minima close to 0, 90 and 180 deg. The shape and amplitude of this function are independent of pattern orientation. It was found that the angle acuity was unaffected by excluding a large portion of the target in the region of the vertex, and that the pattern of dependence of acuity on angle changed radically when the target was reduced ultimately to three blobs that defined the cardinal points of the stimulus. The data suggest that when the target comprises line segments, angle discrimination is not limited by noise that arises at early levels of processing and that angle perception is mediated by mechanisms that are specialized for the perception of image geometry. An opponent process model, that is based on the combined outputs of just two types of filter, is proposed as the basis for the perception of image geometry. This type of system is appropriate for computing one of the differential invariants in an optic flow field. Copyright © 1996 Elsevier Science Ltd.

• Orientation acuity for sine-wave gratings with random variation of spatial frequency

  Authors: D.W. Heeley, H.M. Buchanan-Smith, S. Heywood

  Vision Research.

  Orientation discrimination thresholds were estimated for sine-wave grating stimuli using a two-alternative forced-choice procedure on the two principal, and the two main oblique axes. The twoOrientation discrimination thresholds were estimated for sine-wave grating stimuli using a two-alternative forced-choice procedure on the two principal, and the two main oblique axes. The two discriminanda within any trial were subject to independent random variation of their spatial frequency. The variation of spatial frequency was defined by a Gaussian probability density function. Thresholds were obtained for five different depths of frequency variation within the range 0.0–1.0 octave. We find that orientation acuity on any of the axes tested is unaffected by variation in the spatial frequency of the targets. The data support the hypothesis that orientation and spatial frequency are independent and orthogonal neural codes.

• Recognition of stimulus orientation

  Authors: D.W. Heeley, H.M. Buchanan-Smith

  Vision Research.

  The threshold for detecting a deviation in the orientation of a test stimulus from vertical and from horizontal was measured with a single test interval. The test stimuli were step edges, thin lines,The threshold for detecting a deviation in the orientation of a test stimulus from vertical and from horizontal was measured with a single test interval. The test stimuli were step edges, thin lines, and sine wave gratings of 2.5, 5.0 and 10.0 c/deg. Recognition thresholds were found to be independent of the frequency content and nature of the test stimulus. The average threshold value on the principal meridians was found to be approx. 0.6 deg. Additional testing was conducted with two interval forced choice designs, both with and without random perturbation of the orientation of the stimuli. Random perturbation of orientation reduces acuity estimates. The results are compared with those obtained by testing on the oblique meridia. We conclude that the meridional anisotropy of orientation discrimination, which favours the vertical and horizontal is a result, in part, of the influence of non-visual mechanisms.

• Evidence for separate, task dependent noise processes in orientation and size perception

  Authors: D.W. Heeley, H.M. Buchanan-Smith

  Vision Research.

  Spatial acuity was estimated as the minimum difference in target spatial frequency which could act as a cue in a double concurrent, single interval orientation discrimination task. Experiments wereSpatial acuity was estimated as the minimum difference in target spatial frequency which could act as a cue in a double concurrent, single interval orientation discrimination task. Experiments were conducted with vertical and oblique (45 deg) targets at three different spatial frequencies covering a range of two octaves. Frequency thresholds were found to be lower than those estimated by conventional methods by a factor of nearly 50%. They followed Weber's law for target frequency and were independent of target orientation. The orientation thresholds exhibited a normal oblique effect, and were not affected by the simultaneous judgements of target frequency. The data support the contention that the neural codes for image size and image orientation are segregated at an early stage of processing, and that the main source of noise that limits the precision of coding in these domains exists beyond the level of early mechanisms.

• Changes in the perceived direction of drifting plaids, induced by asymmetrical changes in the spatio-temporal structure of the underlying components

  Authors: D.W. Heeley, H.M. Buchanan-Smith

  Vision Research.

  When a plaid pattern with symmetrical velocity components (Type I) is changed to a plaid pattern with asymmetrical velocity components (Type IA), the overall direction of drift appears to undergo aWhen a plaid pattern with symmetrical velocity components (Type I) is changed to a plaid pattern with asymmetrical velocity components (Type IA), the overall direction of drift appears to undergo a rotation without any other change to the spatial parameters of the components. This change in the perceived drift direction can be induced by altering either the temporal frequency of the components or by altering their spatial frequency. In separate experiments, we have estimated the magnitude of the temporal and spatial frequency thresholds that are necessary to create a liminal change in direction of this type. The results from both temporal and spatial frequency experiments are closely similar. We find that liminal rotations can be induced by changes in the spatio-temporal structure of the sine-wave grating components that are undetectable when these components are presented in isolation. Further, we find that the “velocity threshold for direction” is not a constant factor, but critically depends on the relative orientation of the two elements that form the plaid. Forced-choke experiments were also conducted to estimate the extent of the apparent rotation of the plaid pattern for differing levels of asymmetry in the spatial frequency and temporal frequency of the components. The magnitude of the pattern rotation is predicted by a model of motion direction that encodes the successive displacements of the intersections of the gratings. Finally, we demonstrate that the velocity thresholds for perceived rotation exhibit a meridional anisotropy that depends on the direction of drift of the overall pattern and not on the orientation of the components. Taken together, the results support the view that, unlike speed discrimination, the main limiting factor in the perception of motion direction is not at the level at which the components are extracted, but is at or beyond the level of pattern analysis. The two constituents of the pattern motion vector, speed and direction, are computed independently.