Biomedical subjects

Ernest Greene

Publications and source records attributed to Ernest Greene.

5 recordsLinked to original sources

PubMed2006

Simultaneity in the millisecond range as a requirement for effective shape recognition.

Neurons of the visual system are capable of firing with millisecond precision, and synchrony of firing may provide a mechanism for "binding" stimulus elements in the image for purposes of recognition. While the neurophysiology is suggestive, there has been relatively little behavioral work to support the proposition that synchrony contributes to object recognition. The present experiments examined this issue by briefly flashing dots that were positioned at the outer boundary of namable objects, similar to silhouettes. Display of a given dot lasted only 0.1 ms, and temporal proximity of dot pairs, and among dot pairs, was varied as subjects were asked to name each object. In Exp 1, where the display of dots pairs was essentially simultaneous (0.2 ms to show both), there was a linear decline in recognition of the shapes as the interval between pairs increased from 0 ms to 6 ms. Compared with performance at 0 ms of delay, even the 2 ms interval between pairs produced a significant decrease in recognition. In Exp 2 the interval between pairs was constant at 3 ms, and the interval between pair members was varied. Here also a linear decline was observed as the interval between pair members increased from 0 ms to 1.5 ms, with the difference between 0 ms and 0.5 ms being significant. Thus minimal transient discrete cues can be integrated for purposes of shape recognition to the extent that they are synchronously displayed, and coincidence in the millisecond and even submillisecond range is needed for effective encoding of image data.

Journal Article↗

PubMed2005

Do rotation coordinates provide the substrate for a mental protractor?

In previous studies, we have found that the accuracy in judging collinearity of lines or dots varies considerably from one subject to another as a function of the relative angle of the stimulus elements. A model of errors generally shows large excursions across several subranges of angular position. These do not appear to be motor errors, at least not ones that are well separated from perceptual mechanisms. The errors are most likely generated at primary visual cortex, or beyond. We examined and modeled accuracy in judging collinearity of dot pairs, varying the angular position of the dots through 360 degrees, the distance between the dots (stimulus span), and the distance at which the subject was required to respond (response span). Subjects manifested idiosyncratic profiles of error across angular positions, as reported previously. But across the tested range of spans, from 4 to 8 deg, the errors tended to be the same, irrespective of stimulus or response span. This suggests that the judgments are based on a radial (angular) measure of spatial position. We discuss these results in the context of proposals that the brain maps spatial position using rotation coordinates. These new data are consistent with the hypothesis that subjects use the z-axis coordinates as a mental protractor for judging angular position and collinearity.

Humans↗

PubMed2004

Modeling judgments of linear extent.

Subjects were asked to make judgments of linear extent, specifically. to assess and reproduce the span between dots, with distances that ranged from 0.5 to 8degrees of visual angle. The errors of judgment were modeled by regressing against linear and Fourier components, yielding a model for each of the 25 subjects who participated in the five experiments and for each session in which the subjects were tested. Most of the models manifested a complex profile of underestimates and overestimates of span as a function of the span being judged. Successive cycles of under- and over-estimation of spans appeared as quasiperiodic oscillations in. some of the models. We hypothesize that spatial position is encoded by neuron receptive fields that are organized as a mosaic, and these judgment errors may reflect defects in or competitive interaction among these receptive fields.

Humans↗

PubMed2003

Mapping is not sufficient for specifying position in visual space.

The general view is that one knows where an object is located in visual space on the basis of which neurons it activates. But there is reason to believe that a radically different method of specifying position is needed, one which identifies the position using coordinates. Those who study motor systems assume such coordinates, but the question of how the sensory system could derive these values is given no attention.

Attention↗

PubMed2002

Observation distance and recognition of photographs of celebrities' faces.

Subjects were tested to assess the distance at which they could recognize the faces of celebrities (more specifically, a set of 44 portrait photographs of movie and television actors). The set of test photographs was shown initially at a distance of 200 ft. and then closer in increments of 20 ft. When the actor in a given photograph was identified, either by name, character role, or by the movie or television show in which the actor had starred, the recognition-distance was recorded and the photograph was removed from the test set. Those which were not recognized (even at the closest distance) were not included in the data summaries or statistical analysis. In calculating recognition-distance for each photograph, the values were adjusted to reflect the distance at which recognition would have occurred if all the faces were of normal size. The upper limit for recognition, as defined by the distance above which only 10% of the faces are identified, was just over 160 ft. for women, and just under 200 ft. for men. There was also a significant difference in mean recognition distance between women and men. The large range of recognition-distance (across photographs and across subjects) argues that the distance is not controlled primarily by the feature detail provided in a given photograph or by the discrimination and recall skills of the observer. More likely it is a function of diverse memory associations, so that the distance at which each photograph is recognized will depend on such factors as frequency and recency of exposure, perceived attractiveness, and how much the subject admires the celebrity.

Adult↗