<p>Gaze tracking is the estimation of the point in space a person is “looking at”. This is widely used in both diagnostic and interactive applications, such as visual attention studies and human-computer interaction. The most common commercial solution used to track gaze today uses a combination of infrared illumination and one or more cameras. These commercial solutions are reliable and accurate, but often expensive. The aim of this thesis is to construct a simple single-camera gaze tracker from off-the-shelf components. The method used for gaze tracking is based on infrared illumination and a schematic model of the human eye. Based on images of reflections of specific light sources in the surfaces of the eye the user’s gaze point will be estimated. Evaluation is also performed on both the software and hardware components separately, and on the system as a whole. Accuracy is measured in spatial and angular deviation and the result is an average accuracy of approximately one degree on synthetic data and 0.24 to 1.5 degrees on real images at a range of 600 mm.</p>

Reading requires the orchestration of visual, attentional, language-related, and oculomotor processing constraints. This study replicates previous effects of frequency, predictability, and length of fixated words on fixation durations in natural reading and demonstrates new effects of these variables related to previous and next words. Results are based on fixation durations recorded from 222 persons, each reading 144 sentences. Such evidence for distributed processing of words across fixation durations challenges psycholinguistic immediacy-of-processing and eye-mind assumptions. Most of the time the mind processes several words in parallel at different perceptual and cognitive levels. Eye movements can help to unravel these processes.

Emotional interplay and communication with patients diagnosed with schizophrenia was studied in clinical interviews. Fifty-one video recorded interviews were conducted by two psychologists with nine patients. Qualitative and quantitative methods were used in three successive studies. Study I examined the communicative interplay on an overall level, including verbal and nonverbal means of communication. The interviewer’s willingness to explore and pursue the emotional content in the patient’s narrative was found to be important for establishing well functioning communication. In Study II, the stability over time of facial affective expressions in the emotional interplay was evaluated, using EMFACS. For the patients, no substantial changes in the amount of affects were found across all the interview occasions, although for one interviewer, contempt slightly increased. Whereas previous findings found contempt to be the most frequent affect in patients, in the present material disgust was as common, but depended on the interviewer. Study III investigated gaze behaviour and facial affective expressiveness. The objective was to test whether patients reduced their negative facial affectivity during mutual gaze. The patients were found to not reduce their negative facial affectivity during the state of mutual gaze. This finding was independent of both interview occasion and interviewer and implies that the patients might have intended to communicate negative facial affectivity to the interviewer. The research suggests that the emotional interplay is dominated by the negative facial affective expressions of mainly disgust and contempt. It is proposed that these negative affects may be connected to a patient’s low self-esteem, as the self in schizophrenia may be engrained by self-disgusting and self-contemptive affective experiences. The interviewer’s capacity to respond to these negative facial expressions must therefore be considered as important.

The photographic work of contemporary Moroccan artist, Lalla Essaydi, embodies a new artistic hybridity that reflects her nomadic, globalized background. With this work, the artist employs visual symbolism and uses multiple forms of artistic media as a means to analyze her multicultural background. Throughout her series, which spans 2004-present, Essaydi uses both literal and metaphorical representations of space and self as a means to examine the multifacetedness of her national identity and the many gazes that define that identity. She uses artistic production as a means of mediating the collective experiences of her identity in order to negotiate and construct a revised image of self.

In four experiments we used eye-tracking to investigate biases in looking behaviour during visual decision making tasks. In Experiment 1, participants viewed arrays of images of photographic art and decided which image was preferred (from a set of either two or eight alternatives). To analyze gaze behaviour during the decision we identified dwells (where a dwell is a series of consecutive fixations on a decision alternative). This analysis revealed two forms of gaze bias in the period prior to the response. Replicating prior findings (Shimojo, Simion, Shimojo, & Scheier, 2003), just prior to the response we found an increase in the frequency of dwells on the chosen item. In addition, throughout the decision, dwells on the chosen item were longer than dwells on other items. This pattern of biases was extremely similar across preference and non-preference decision instructions, but overall the biases were more pronounced in eight alternative decisions than in two alternative decisions. In Experiment 2 we manipulated the number of decision alternatives while controlling for differences in the stimulus displays. Participants viewed displays containing six everyday items, and chose either which of two sets of three items was the most expensive (two alternative set selection task) or which of the six items was the most expensive (six alternative item selection task). Consistent with Experiment 1, participants exhibited greater selectivity in their processing of stimulus information in the six alternative decisions compared to the two alternative decisions. In Experiments 3 and 4 we manipulated stimulus exposure in order to test predictions derived from the Gaze Cascade model (Shimojo et al., 2003). In Experiment 3, participants performed an eight alternative decision in which four of the items had been pre-exposed prior to the decision. In Experiment 4, stimulus exposure was manipulated during the ongoing decision using a gaze-contingent methodology. While these manipulations of stimulus exposure had strong effects on gaze bias, the specific predictions of the model were not supported. Rather, we suggest an interpretation based on prior research, according to which the gaze bias reflects the selective processing of stimulus information according to its relevance to the decision task.

Quantitative relationships were established between speech intelligibility and gaze patterns when subjects listened to sentences spoken by a single talker at different auditory SNRs while viewing one or more talkers. When the auditory SNR was reduced and subjects moved their eyes freely, the main gaze strategy involved looking closer to the mouth. The natural tendency to move closer to the mouth was found to be consistent with a gaze strategy that helps subjects improve their speech intelligibility in environments that include multiple talkers. With a single talker and a fixed point of gaze, subjects' speech intelligibility was found to be optimal for fixations that were distributed within 10 degrees of the center of the mouth. Lower performance was observed at larger eccentricities, and this decrease in performance was investigated by mapping the reduced acuity in the peripheral region to various levels of spatial degradation.

Quantitative relationships were established between speech intelligibility and gaze patterns when subjects listened to sentences spoken by a single talker at different auditory SNRs while viewing one or more talkers. When the auditory SNR was reduced and subjects moved their eyes freely, the main gaze strategy involved looking closer to the mouth. The natural tendency to move closer to the mouth was found to be consistent with a gaze strategy that helps subjects improve their speech intelligibility in environments that include multiple talkers. With a single talker and a fixed point of gaze, subjects' speech intelligibility was found to be optimal for fixations that were distributed within 10 degrees of the center of the mouth. Lower performance was observed at larger eccentricities, and this decrease in performance was investigated by mapping the reduced acuity in the peripheral region to various levels of spatial degradation.

An individual`s eyes provide a wealth of information during social interactions. The present research investigates the social adjustment implications of one gaze behaviour, specifically, shared attention, which is the tendency to follow an interlocutor`s directed gaze to attend to the same object or location. Recent clinical research suggested that gaze control reflects the capacity to differentiate self from other at the attentional level, since patient populations with poor gaze control abilities (i.e., schizophrenic patients) were also found to exhibit difficulty in differentiating between the self and another agent. Four studies were conducted to examine whether flexible gaze following behavior, specifically the ability to inhibit gaze-following, when the situation warrants, would be positively linked with two markers of adaptive social functioning: sociocognitive abilities and self-close other(s) differentiation. Based on previous research that gaze cues linked to upright (but not inverted) faces trigger reflexive gaze following mechanisms, an upright face condition was used to assess social cueing mechanisms and an inverted face condition, as a control for non-social cueing mechanisms in a gaze control task with realistic (Study 2) and schematic faces (Studies 1, 3, and 4). Studies 1-4 showed that more flexible gaze following behavior predicted superior sociocognitive abilities, as indexed by higher capacity to infer the mental states of others in both young and older adults (Studies 1-3), as well as in clinical populations (i.e., Parkinson’s Disease [PD] patients, Study 4). Studies 2-4 further revealed that poorer gaze control predicted decreased self-close other differentiation in both younger and older adults. In Study 2, poorer gaze control performance characterized young adults from enmeshed family systems, which allow limited private space and emotional autonomy. In Studies 3 and 4, poorer gaze control predicted decreased cognitive-affective differentiation from one’s spouse and lower marital quality in healthy elderly couples (Study 3) and elderly couples, where one spouse had PD (Study 4). The present findings argue for the existence of a unified sociocognitive network, perpetually shaped by one’s interpersonal history, and which encompasses perceptual mechanisms, specialized for face and gaze processing and higher-order cognitive mechanisms, specialized for processing the meaning (s) of social environments.

In four experiments we used eye-tracking to investigate biases in looking behaviour during visual decision making tasks. In Experiment 1, participants viewed arrays of images of photographic art and decided which image was preferred (from a set of either two or eight alternatives). To analyze gaze behaviour during the decision we identified dwells (where a dwell is a series of consecutive fixations on a decision alternative). This analysis revealed two forms of gaze bias in the period prior to the response. Replicating prior findings (Shimojo, Simion, Shimojo, & Scheier, 2003), just prior to the response we found an increase in the frequency of dwells on the chosen item. In addition, throughout the decision, dwells on the chosen item were longer than dwells on other items. This pattern of biases was extremely similar across preference and non-preference decision instructions, but overall the biases were more pronounced in eight alternative decisions than in two alternative decisions. In Experiment 2 we manipulated the number of decision alternatives while controlling for differences in the stimulus displays. Participants viewed displays containing six everyday items, and chose either which of two sets of three items was the most expensive (two alternative set selection task) or which of the six items was the most expensive (six alternative item selection task). Consistent with Experiment 1, participants exhibited greater selectivity in their processing of stimulus information in the six alternative decisions compared to the two alternative decisions. In Experiments 3 and 4 we manipulated stimulus exposure in order to test predictions derived from the Gaze Cascade model (Shimojo et al., 2003). In Experiment 3, participants performed an eight alternative decision in which four of the items had been pre-exposed prior to the decision. In Experiment 4, stimulus exposure was manipulated during the ongoing decision using a gaze-contingent methodology. While these manipulations of stimulus exposure had strong effects on gaze bias, the specific predictions of the model were not supported. Rather, we suggest an interpretation based on prior research, according to which the gaze bias reflects the selective processing of stimulus information according to its relevance to the decision task.

An individual`s eyes provide a wealth of information during social interactions. The present research investigates the social adjustment implications of one gaze behaviour, specifically, shared attention, which is the tendency to follow an interlocutor`s directed gaze to attend to the same object or location. Recent clinical research suggested that gaze control reflects the capacity to differentiate self from other at the attentional level, since patient populations with poor gaze control abilities (i.e., schizophrenic patients) were also found to exhibit difficulty in differentiating between the self and another agent. Four studies were conducted to examine whether flexible gaze following behavior, specifically the ability to inhibit gaze-following, when the situation warrants, would be positively linked with two markers of adaptive social functioning: sociocognitive abilities and self-close other(s) differentiation. Based on previous research that gaze cues linked to upright (but not inverted) faces trigger reflexive gaze following mechanisms, an upright face condition was used to assess social cueing mechanisms and an inverted face condition, as a control for non-social cueing mechanisms in a gaze control task with realistic (Study 2) and schematic faces (Studies 1, 3, and 4). Studies 1-4 showed that more flexible gaze following behavior predicted superior sociocognitive abilities, as indexed by higher capacity to infer the mental states of others in both young and older adults (Studies 1-3), as well as in clinical populations (i.e., Parkinson’s Disease [PD] patients, Study 4). Studies 2-4 further revealed that poorer gaze control predicted decreased self-close other differentiation in both younger and older adults. In Study 2, poorer gaze control performance characterized young adults from enmeshed family systems, which allow limited private space and emotional autonomy. In Studies 3 and 4, poorer gaze control predicted decreased cognitive-affective differentiation from one’s spouse and lower marital quality in healthy elderly couples (Study 3) and elderly couples, where one spouse had PD (Study 4). The present findings argue for the existence of a unified sociocognitive network, perpetually shaped by one’s interpersonal history, and which encompasses perceptual mechanisms, specialized for face and gaze processing and higher-order cognitive mechanisms, specialized for processing the meaning (s) of social environments.