Jessie J. Peissig

The role of surface pigmentation for recognition revealed by contrast reversal in faces and Greebles

Faces are difficult to recognize when viewed as negatives [Galper (1970). Recognition of faces in photographic negative. Psychonomic Science, 19, 207]. Here we examined the contribution of surface properties to this contrast effect, and whether it is modulated by object category. We tested observers in a matching task using faces or Greebles, presented with or without pigmentation. When stimulus pairs were shown with mismatched contrast (e.g., positive-negative), there was a decrement in performance. This decrement was larger when the stimuli were shown with pigmentation, and this difference was more pronounced with faces than with Greebles. Overall, contrast reversal disrupts the recognition of both faces and objects to a greater degree in the presence of pigmentation, suggesting that surface properties are important components of the object representation.

Recognizing disguised faces

Across three experiments, we evaluated the effects of “disguises” on observers’ face identification performance using naturalistic images in which individuals posed with a variety of wigs and eyeglasses. Experiment 1 tested recognition memory performance with and without disguises and showed that any changes in these facial attributes hindered performance, replicating previous findings. More interestingly, Experiment 1 revealed that a change in hairstyle or the removal of eyeglasses had more impact on performance than did the addition of eyeglasses. In Experiment 2, disguised and undisguised faces were presented upright or inverted to examine whether the performance decrements seen in Experiment 1 were attributable to disruption of processing strategies for faces. Despite showing an overall effect of disguise on performance, there was no interaction between inversion and disguise. This suggests that disguises are not directly affecting processing strategies, but instead disguises are likely encoded as part of the overall representation. Similarly, in Experiment 3, the composite face paradigm was used to examine whether the impact of disguises is attributable to disruption of holistic processing for faces. Again, we found an overall effect of disguise on performance, but here we also observed that the presence of disguises interacted with participants’ tendency to form holistic face representations.

Is region-of-interest overlap comparison a reliable measure of category specificity?

Analysis of the degree of overlap between functional magnetic resonance imagingderived regions of interest (ROIs) has been used to assess the functional convergence and/or segregation of category-selective brain areas. An examination of the extant literature reveals no consistent usage for how such overlap is calculated, nor any systematic comparison between different methods. We argue that how ROI overlap is computed, especially the choice of the denominator in the formula, can profoundly affect the results and interpretation of such an analysis. To do this, we compared the overlap of the FFA-FFA (fusiform face area) and FFA-FGA (fusiform Greeble-selective area) in a localizer study testing both Greeble novices and experts. When using a single ROI as the denominator, we found a significant difference in FFA-FFA versus FFA-FGA overlap, consistent with the result of a previous study arguing for face specificity of the FFA [Rhodes, G., Byatt, G., Michie, P. T., & Puce, A. Is the fusiform face area specialized for faces, individuation, or expert individuation? J Cogn Neurosci, 16, 189203, 2004]. However, these ROI overlap differences disappeared when the denominator combined both of the involved ROIs, and the patterns of such overlap comparisons were dependent on given statistical thresholds. We also found proportionally decreasing FFA-FFA overlap with increasing center-of-FFA distance, resolving an apparent contradiction between the consistency of the location of the FFA and the seemingly low FFA-FFA overlap. Finally, Monte Carlo simulations revealed the most stable formulathe most resistant to ROI size variationsto be the average of the two single-ROI-denominator-based overlap indices. In sum, ROI overlap analysis is not a reliable tool for assessing category specificity, and caution should be exercised with regard to ROI overlap definition, underlying assumptions, and interpretation.

Effects of Varying Stimulus Size on Object Recognition in Pigeons

The authors investigated the pigeons ability to generalize object discrimination performance to smaller and larger versions of trained objects. In Experiment 1, they taught pigeons with line drawings of multipart objects and later tested the birds with both larger and smaller drawings. The pigeons exhibited significant generalization to new sizes, although they did show systematic performance decrements as the new size deviated from the original. In Experiment 2, the authors tested both linear and exponential size changes of computer-rendered basic shapes to determine which size transformation produced equivalent performance for size increases and decreases. Performance was more consistent with logarithmic than with linear scaling of size. This finding was supported in Experiment 3. Overall, the experiments suggest that the pigeon encodes size as a feature of objects and that the representation of size is most likely logarithmic.

Superordinate Categorization Via Learned Stimulus Equivalence: Quantity of Reinforcement, Hedonic Value, and the Nature of the Mediator

Three experiments examined superordinate categorization via stimulus equivalence training in pigeons. Experiment 1 established superordinate categories by association with a common number of food pellet reinforcers, plus it established generalization to novel photographic stimuli. Experiment 2 documented generalization of choice responding from stimuli signaling different numbers of food pellets to stimuli signaling different delays to food reinforcement. Experiment 3 indicated that different numbers of food pellets did not substitute as discriminative stimuli for the photographic stimuli with which the food pellets had been paired. The collective results suggest that the effective mediator of superordinate categories that are established via learned stimulus equivalence is not likely to be an accurate representation of the reinforcer, neither is it likely to be a distinctive response that is made to the discriminative stimulus. Motivational or emotional mediation is a more likely account.

Learning an object from multiple views enhances its recognition in an orthogonal rotational axis in pigeons

In the natural environment, most objects are seen from several different viewpoints. We explored the nature of recognition after training with multiple views and compared it to recognition after training with only one view. Pigeons were taught with either five views or one view of each of four single-geon objects. Pigeons trained with five views responded more accurately to novel views of an object than did pigeons trained with only one view. This result held even when the novel views came from a rotational axis that was orthogonal to the training axis. These results do not accord with recognition processes involving mental rotation or direct interpolation. Pigeons trained with five views may have formed a view-invariant representation [Psychol. Rev. 94 (1987) 115; Vision Res. 39 (1999) 2885]; alternatively, they may have acquired a more detailed shape space of the objects in which to measure object similarity [Representation and recognition in vision, MIT Press, MA, 1999], or learned to attend to a broader range of features of each object [J. Exp. Anal. Behav. 54 (1990) 69].

Discrimination of geons by pigeons: The effects of variations in surface depiction

We explored how changes in the depiction of the surface features of a simple volume (a geon) affected the pigeon’s recognition performance. Pigeons were trained to make a different keypeck response to each of four computer-rendered single-geon objects. In Experiment 1, the pigeons were tested with images of the original stimuli in which the light source was shifted from its original position, as well as with silhouettes and line drawings of these objects. All three types of stimulus variations resulted in marked drops in performance: above chance for silhouettes and light-change stimuli, but at chance for line drawings. In Experiment 2, the pigeons were tested with images of the original stimuli in which the contrast levels were either increased or decreased. These transformations resulted in very small drops in performance (except for the complete absence of contrast-a silhouette). These results indicated that the pigeons attended to the shape of the outside contour of an object and to the relative brightness of an object’s surface contours.

XOR style tasks for testing visual object processing in monkeys

Using visually complex stimuli, three monkeys learned visual exclusive-or (XOR) tasks that required detecting two way visual feature conjunctions. Monkeys with passive exposure to the test images, or prior experience, were quicker to acquire an XOR style task. Training on each pairwise comparison of the stimuli to be used in an XOR task provided nearly complete transfer when stimuli became intermingled in the full XOR task. Task mastery took longer, accuracy was lower, and response times were slower for conjunction stimuli. Rotating features of the XOR stimuli did not adversely effect recognition speed or accuracy.

Using the reassignment procedure to test object representation in pigeons and people.

In four experiments, we evaluated Lea’s (1984) reassignment procedure for studying object representation in pigeons (Experiments 1–3) and humans (Experiment 4). In the initial phase of Experiment 1, pigeons were taught to make discriminative button responses to five views of each of four objects. Using the same set of buttons in the second phase, one view of each object was trained to a different button. In the final phase, the four views that had been withheld in the second stage were shown. In Experiment 2, pigeons were initially trained just like the birds in Experiment 1. Then, one view of each object was reassigned to a different button, now using a new set of four response buttons. In Experiment 3, the reassignment paradigm was again tested using the number of pecks to bind together different views of the same object. Across all three experiments, pigeons showed statistically significant generalization of the new response to the non-reassigned views, but such responding was well below that to the reassigned view. In Experiment 4, human participants were studied using the same stimuli and task as the pigeons in Experiment 1. People did strongly generalize the new response to the non-reassigned views. These results indicate that humans, but not pigeons, can employ a unified object representation that they can flexibly map to different responses under the reassignment procedure.

The Use of Eyebrows as a Visual Feature.

Previous research suggests that although faces are processed holistically, concealing or erasing parts of the face impairs recognition. Recent research suggests that eyebrows play a key role in facial recognition (Sadr, Jarudi, & Sinha, 2003). What has yet to be understood is what exactly that role is. Eyebrows may serve as placeholders, to measure spatial distances within the face (White, 2004). If so, then changing eyebrows will have no effect on recognition, so long as the eyebrows remain in the same position. Eyebrows may also be used as recognition features of the face. If this is the case, altering eyebrows will impair recognition. Seventy-two participants were tested with faces on a same/different task. Participants were presented with two faces sequentially and reported whether the two individuals were the same or different. There were four conditions for the two faces presented: Same faces (no changes), different faces (no changes), same faces with different eyebrows, or different faces with the same eyebrows. When eyebrows were replaced, the new eyebrows were placed in the same position as the original eyebrows. Testing consisted of 320 trials, 80 trials in each condition. It was expected that if eyebrows are used as a feature for recognition, then having different eyebrows on the same trials and the same eyebrows on different trials should both yield poorer performance. Results confirmed these predictions (see Figure 1), showing a significant difference between same trials with the original face and same trials with changed eyebrows. We also found a significant difference between different trials with the original faces and different trials in which the eyebrows were the same. These results show that participants attend not only to the location of the eyebrows but also their visual appearance, suggesting that they could serve a role as visual feature of face recognition. Meeting abstract presented at VSS 2015.