Memory fixation control device and memory fixation method

Abstract

To fix a memory efficiently to a subject.SOLUTION: A memory fixing control apparatus includes an acquisition part for acquiring brain activity information showing the active state of a brain of a subject, a determination part for determining a sleeping level showing the depth of sleep of the subject, and determining the active state of a prescribed portion of the brain of the subject based on the acquired brain activity information, and a reproduction control part for allowing a reproducer to reproduce a content stimulating a hearing sensation of the subject according to a determination result by the determination part.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a memory fixing control device and a memory fixing method. [Background technology]

[0002] BACKGROUND ART There is known a technique for enhancing the cognitive domain of a subject by providing sensory stimulation to the subject in a sleeping state (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2021-503339 Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in Patent Document 1 provides sensory stimuli regardless of the brain activity state of the subject, making it difficult to efficiently consolidate memories in the subject. Therefore, a technology for efficiently consolidating memories in the subject is needed.

[0005] The present invention has been made in view of the above, and has as its object to provide a memory consolidation control device and a memory consolidation method that can efficiently consolidate memories in a subject. [Means for solving the problem]

[0006] The memory consolidation control device of the present invention comprises an acquisition unit that acquires brain activity information indicating the activity state of the subject's brain, a judgment unit that determines the sleep level indicating the depth of the subject's sleep and determines the activity state of a specific part of the subject's brain based on the acquired brain activity information, and a playback control unit that causes a playback device to play content that stimulates the subject's hearing depending on the judgment result of the judgment unit.

[0007] The memory consolidation method of the present invention includes acquiring brain activity information indicating the activity state of a subject's brain, determining a sleep level indicating the depth of the subject's sleep, determining the activity state of a specific part of the subject's brain based on the acquired brain activity information, and playing content that stimulates the subject's hearing on a playback device according to the determination result. [Effects of the Invention]

[0008] According to the present invention, it is possible to efficiently solidify memories in subjects. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing an example of a memory fixing device according to the present embodiment. [Figure 2] FIG. 2 is a functional block diagram showing an example of the memory fixing device according to the present embodiment. [Figure 3] FIG. 3 is a diagram showing an example of sleep levels. [Figure 4] FIG. 4 is a graph showing an example of the change over time in the oxygenated hemoglobin concentration of a subject. [Figure 5] FIG. 5 is a diagram showing an example of time-dependent changes in the sleep level of a subject. [Figure 6] FIG. 6 is a flowchart showing an example of the operation of the control device. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of a memory fixation control device and a memory fixation method according to the present invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments. Furthermore, the components in the following embodiments include those that are easily replaceable by those skilled in the art, or those that are substantially the same.

[0011] Fig. 1 is a schematic diagram showing an example of a memory fixing device 100 according to this embodiment. Fig. 2 is a functional block diagram showing an example of a memory fixing device 100 according to this embodiment.

[0012] As shown in FIGS. 1 and 2, the storage fixing device 100 includes a detection device 10, a setting device 20, a control device (storage fixing control device) 30, and a playback device 40.

[0013] The detection device 10 detects brain activity information indicating the activity state of the subject's brain. As the detection device 10, for example, a measurement device that measures cerebral blood flow based on the principle of fNIRS (functional Near-Infrared Spectroscopy) is used. Note that the detection device 10 is not limited to a measurement device based on the principle of fNIRS, and for example, a measurement device that measures based on the principle of fMRI (functional Magnetic Resonance Imaging) that measures brain activity as brain activity information may be used.

[0014] The detection device 10 includes, for example, a head-mounted unit 11, a plurality of optical fiber channels 12, and an information generating unit 13. The head-mounted unit 11 is attached to the head of the subject. The optical fiber channel 12 includes an emitting optical fiber 12a that emits near-infrared light from a light source (not shown) to the subject's head, and a receiving optical fiber 12b that receives near-infrared light reflected or scattered inside the subject's head and sends the light to the information generating unit 13. The optical fibers 12a and 12b are positioned at positions that allow measurement of the Wernicke's area and Broca's area of ​​the subject's brain.

[0015] The information generating unit 13 calculates the oxygenated hemoglobin concentration as brain activity information based on the near-infrared light transmitted from the light-receiving optical fiber 12b. The information generating unit 13 may calculate at least one of the deoxygenated hemoglobin concentration and the total hemoglobin concentration as brain activity information, in addition to or instead of the oxygenated hemoglobin concentration. In this embodiment, the brain activity information calculated by the information generating unit 13 is activity information about the Wernicke's area and Broca's area of ​​the subject's brain. The optical fiber 12b and the information generating unit 13 may be connected by wire or wirelessly. The information generating unit 13 may be built into the head-mounted unit 11.

[0016] The setting device 20 inputs setting information for the memory fixing device 100. The setting information includes, for example, information about the content to be played back by the playback device 40. The setting device 20 may be an input device such as a keyboard or a mouse, or may be a smartphone or tablet with a touch panel.

[0017] The control device 30 comprehensively controls the operation of the memory fixing device 100. The control device 30 has a processing device such as a CPU (Central Processing Unit) and a storage device such as a RAM (Random Access Memory) or a ROM (Read Only Memory). The control device 30 has an acquisition unit 31, a determination unit 32, a playback control unit 33, and a storage unit 34.

[0018] The acquisition unit 31 acquires the brain activity information generated by the information generation unit 13 of the detection device 10. The acquisition unit 31 may be configured to have the functions of the information generation unit 13 described above. In other words, the acquisition unit 31 may be configured to directly acquire a signal sent from the optical fiber 12b of the detection device 10 and calculate the brain activity information. The acquisition unit 31 acquires the brain activity information at predetermined intervals.

[0019] The determination unit 32 determines the sleep level of the subject. The timing at which the determination unit 32 determines the sleep level may be the same as or correspond to the timing at which the acquisition unit 31 acquires the brain activity information, or may be different from or not correspond to the timing at which the acquisition unit 31 acquires the brain activity information.

[0020] 3 is a diagram showing an example of sleep levels. As shown in FIG. 3, in this embodiment, the sleep levels can be set to six levels, for example, level 0 for an awake state (a state that is not asleep), level 1 for REM sleep, level 2 for stage 1 of non-REM sleep, level 3 for stage 2 of non-REM sleep, level 4 for stage 3 of non-REM sleep, and level 5 for stage 4 of non-REM sleep. Note that the sleep level settings are not limited to the above and may be set to, for example, five or fewer levels or seven or more levels. The determination unit 32 may determine the sleep level using brain activity information acquired by the acquisition unit 31, or may determine the sleep level using brain waves and heart rate detected by an electroencephalograph or heart rate monitor, or movements or vibrations of the person during sleep detected by a three-axis acceleration sensor or the like.

[0021] The determination unit 32 determines the activity state of a predetermined region of the subject's brain based on the brain activity information acquired by the acquisition unit 31. The timing at which the determination unit 32 determines the activity information can be, for example, the same as or corresponding to the timing at which the acquisition unit 31 acquires the brain activity information. In this embodiment, the predetermined region of the brain is, for example, Wernicke's area and Broca's area. The activity state can be set to two stages: an adaptive state (predetermined state) that is suitable for memory consolidation, and a non-adaptive state that is not suitable for memory consolidation.

[0022] Figure 4 shows an example of the change in the oxygenated hemoglobin concentration of a subject over time. When brain cells are active, oxygen molecules are released from the oxygenated hemoglobin in the blood (deoxidation), converting it to deoxygenated hemoglobin, and the oxygen molecules produced by deoxidation are transported to brain cells. In other words, a state in which the oxygenated hemoglobin concentration is low and the deoxygenated hemoglobin concentration is high can be recognized as a state in which brain cells are actively active and deoxygenation is occurring actively. On the other hand, a state in which the oxygenated hemoglobin concentration is high and the deoxygenated hemoglobin concentration is low can be recognized as a state in which deoxygenation is not occurring as actively and brain cells have ample room for activity.

[0023] Therefore, as shown in FIG. 4, for example, the judgment unit 32 can judge an adaptive state when the oxyhemoglobin concentration in both the Wernicke's area and the Broca's area of ​​the brain is equal to or greater than a predetermined value (thresholds A1 and A2, respectively), and can judge an adaptive state when the oxyhemoglobin concentration in at least one of the Wernicke's area and the Broca's area of ​​the brain is less than the thresholds A1 and A2, respectively.

[0024] Based on the determination result of the determination unit 32, the playback control unit 33 causes the playback device 40 to play content that stimulates the auditory sense of the subject. In this embodiment, the content is, for example, audio set by the subject using the setting device 20, and includes a first content including details to be memorized by the subject, and a second content different from the first content. Examples of the second content include music related to the content of the first content, music that calms the subject, and advertising audio that appeals to the subject about products and services.

[0025] When the determination unit 32 determines that the sleep level is the first level and that the activity state is the adaptive state, the playback control unit 33 causes the playback device 40 to play the first content as the content. In this embodiment, the first level can be, for example, level 1, where the subject is in REM sleep. During period L (see FIG. 4) in the non-adaptive state, the playback control unit 33 controls so that the first content is not played even if the subject's sleep level is the first level. This avoids placing more strain than necessary on brain cells, allowing memory consolidation to occur efficiently in a state where brain cells have room for activity.

[0026] When the determination unit 32 determines that the sleep level is a second level different from the first level, the playback control unit 33 causes the playback device 40 to play the second content as the content. The second level can be a level of sleep that is deeper than the first level. In this embodiment, the second level can be, for example, a level corresponding to stage 1 or stage 2 of non-REM sleep in the subject, i.e., level 2 or level 3. Note that the playback control unit 33 does not need to cause the playback of the second content. For example, when causing the playback device 40 to play audio of an advertisement as the second content, the playback control unit 33 can start the playback after a predetermined time has elapsed since the determination unit 32 determined that the sleep level of the subject is at the second level, so as not to hinder the memory retention of the details of the first content.

[0027] After causing the playback device 40 to play the first content, the playback control unit 33 stops the first content if the determination unit 32 determines that the sleep level is different from the first level or that the subject's brain activity state is not in an adaptive state. Furthermore, after causing the playback device 40 to play the second content, the playback control unit 33 stops the second content if the determination unit 32 determines that the sleep level is different from the second level.

[0028] The storage unit 34 stores various types of information. The storage unit 34 has storage such as a hard disk drive or a solid state drive. Note that an external storage medium such as a removable disk may be used as the storage unit 34. The storage unit 34 stores programs, data, etc. for executing various processes of the acquisition unit 31, the determination unit 32, and the playback control unit 33 in the control device 30. The storage unit 34 also stores the first content and the second content. The storage unit 34 also stores the setting details set by the setting device 20.

[0029] The memory unit 34 stores a program that causes a computer to execute the following processes: acquiring brain activity information indicating the activity state of the subject's brain; determining the sleep level indicating the depth of the subject's sleep and determining the activity state of a specific part of the subject's brain based on the acquired brain activity information; and, depending on the determination result, causing the playback device 40 to play content that stimulates the subject's hearing.

[0030] The playback device 40 plays back the first content and the second content under the control of the playback control unit 33. The playback device 40 has, for example, a speaker that outputs sound. The speaker may be, for example, mounted on headphones that can be worn on the head of the subject.

[0031] Next, a memory consolidation method using the memory consolidation device 100 configured as described above will be described. The subject wears the head-mounted unit 11 of the detection device 10 on their head and adjusts the position so that the optical fiber channel 12 corresponds to the Wernicke's area and Broca's area of ​​the brain. The subject sleeps in this state. Figure 5 is a diagram showing an example of the change in the subject's sleep level over time. In the example shown in Figure 5, the subject's sleep level gradually changes from level 0, which is an awake state, to a deep sleep state (e.g., level 5), and then repeatedly rises and falls over time.

[0032] The detection device 10 irradiates near-infrared light onto the subject's head from the optical fiber 12a and sends the near-infrared light received by the optical fiber 12b to the information generation unit 13. Based on the near-infrared light sent from the optical fiber 12b, the information generation unit 13 calculates the oxyhemoglobin concentrations in the Wernicke's area and Broca's area of ​​the subject's brain as brain activity information.

[0033] In the control device 30, the acquisition unit 31 acquires the brain activity information generated by the information generation unit 13. The determination unit 32 determines the sleep level of the subject, and determines the activity state of a predetermined part of the subject's brain based on the brain activity information acquired by the acquisition unit 31.

[0034] In the example shown in FIG. 5 , at time t1, the determination unit 32 determines that the subject's sleep level is level 3. In this case, the playback control unit 33 controls the playback device 40 to play the second content C2 as the content. The subject in a level 3 sleep state has their hearing stimulated by the second content C2 played from the playback device 40. For example, when the hearing is stimulated by music related to the content of the first content, memory can be consolidated even in a level 3 or level 4 sleep state. Furthermore, when the hearing is stimulated by music that calms the subject, the subject is put into a calm state, thereby suppressing the accumulation of fatigue. Furthermore, when the hearing is stimulated by advertising audio, the content of a product or service can be efficiently promoted to a subject in a level 3 or level 4 sleep state. After time t1, the determination result of the subject's sleep level remains at level 3 for a certain period of time and then changes to level 2. During this period, the playback control unit 33 continues playing the second content C2.

[0035] Also, at time t2, the determination result of the determination unit 32 on the subject's sleep level changes to level 1. In this case, the playback control unit 33 checks whether the determination result of the subject's activity state by the determination unit 32 is an adaptive state. If it is determined that the subject's activity state is an adaptive state, the playback of the second content C2 is stopped and the playback device 40 plays the first content C1. The subject in REM sleep (level 1 sleep state) has their hearing stimulated by the first content C1 played from the playback device 40. This stimulation causes the content contained in the first content C1 to be fixed in the brain as memory.

[0036] Furthermore, during a period L from time t3 to time t4, the determination result of the determination unit 32 on the subject's activity state is a non-adaptive state. In this case, the playback control unit 33 stops the playback of the first content C1. At time t4, the determination result of the subject's activity state is again an adaptive state. In this case, the playback control unit 33 resumes the playback of the first content C1.

[0037] After the playback of the first content C1 is resumed, the determination result of the subject's sleep level changes to level 2 at time t5. In this case, the playback control unit 33 stops the playback of the first content C1 and starts the playback of the second content C2. After time t5, the determination result of the subject's sleep level remains at level 2 for a certain period of time and then changes to level 3. During this period, the playback control unit 33 continues the playback of the second content C2. Furthermore, at time t6, the determination result of the subject's sleep level changes to level 4. In this case, the playback control unit 33 stops the playback of the second content C2.

[0038] In this way, the playback control unit 33 can provide auditory stimulation to the subject with content that corresponds not only to the subject's sleep level but also to the activity state of a specific part of the brain, by causing the playback device 40 to play the first content and the second content based on the judgment results of the subject's sleep level and the judgment results of the subject's activity state.

[0039] Fig. 6 is a flowchart showing an example of the operation of the control device 30. As shown in Fig. 6, the acquisition unit 31 acquires the brain activity information generated by the information generation unit 13 (step S10). The determination unit 32 determines the sleep level of the subject, and determines the activity state of a predetermined part of the subject's brain based on the brain activity information acquired by the acquisition unit 31 (step S20).

[0040] When the determination unit 32 determines that the sleep level is the first level and the activity state is the adaptive state (Yes in step S30), the playback control unit 33 determines whether the second content is being played back (step S40). When the playback control unit 33 determines that the second content is being played back (Yes in step S40), the playback control unit 33 stops the playback of the second content (step S50). When the playback control unit 33 determines that the second content is not being played back (No in step S40) or has stopped the playback of the second content, the playback control unit 33 determines whether the first content is being played back (step S60). When the playback control unit 33 determines that the first content is not being played back (No in step S60), the playback control unit 33 causes the playback device 40 to play the first content (step S70). When the playback control unit 33 determines that the first content is being played back (Yes in step S60), the playback control unit 33 skips step S70 and ends the process.

[0041] If it is determined in step S30 that the sleep level is not the first level or the activity state is not the adaptive state (No in step S30), the playback control unit 33 determines whether the first content is being played back (step S80).If it is determined that the first content is being played back (Yes in step S80), the playback control unit 33 stops the playback of the first content (step S90).

[0042] If the playback control unit 33 determines that the first content is not being played back (No in step S80) or if the playback of the first content has stopped, the playback control unit 33 determines whether the sleep level determination result is the second level. If the playback control unit 33 determines that the sleep level determination result is the second level (Yes in step S100), the playback control unit 33 determines whether the second content is being played back (step S110). If the playback control unit 33 determines that the second content is not being played back (No in step S110), the playback control unit 33 causes the playback device 40 to play the second content (step S120). If the playback control unit 33 determines that the second content is being played back (Yes in step S110), the playback control unit 33 skips step S120 and ends the process.

[0043] Furthermore, if the playback control unit 33 determines that the sleep level determination result is not the second level (No in step S100), it determines whether the second content is being played back (step S130). If the playback control unit 33 determines that the second content is being played back (Yes in step S130), it stops the playback of the second content (step S140). If the playback control unit 33 determines that the second content is not being played back (No in step S130), it skips step S140 and ends the process.

[0044] As described above, the control device 30 according to this embodiment includes an acquisition unit 31 that acquires brain activity information indicating the activity state of the subject's brain, a judgment unit 32 that determines the sleep level indicating the depth of the subject's sleep and judges the activity state of a specific part of the subject's brain based on the acquired brain activity information, and a playback control unit 33 that causes the playback device 40 to play content that stimulates the subject's hearing, depending on the judgment result of the judgment unit 32.

[0045] In addition, the memory consolidation method according to this embodiment includes acquiring brain activity information indicating the activity state of the subject's brain, determining the sleep level indicating the depth of the subject's sleep, determining the activity state of a specific part of the subject's brain based on the acquired brain activity information, and, depending on the determination result, causing the playback device 40 to play content that stimulates the subject's hearing.

[0046] According to this configuration, in addition to the subject's sleep level, the activity state of specific parts of the subject's brain is determined, and content is played back according to the results of both determinations, so that when the subject is asleep, memory consolidation can be carried out efficiently according to the activity state of the brain.

[0047] In the control device 30 according to this embodiment, the playback control unit 33 plays back the first content including the details to be memorized by the subject when the determination unit 32 determines that the sleep level is the first level and that the activity state is a predetermined state. With this configuration, the first content including the details to be memorized by the subject can be played back at an appropriate timing.

[0048] In the control device 30 according to this embodiment, the first level is REM sleep, and the predetermined state is a state in which the oxygenated hemoglobin concentration in the Wernicke's area and Broca's area of ​​the brain is equal to or greater than a predetermined value. With this configuration, when the subject is in REM sleep, memory consolidation can be efficiently achieved according to the activity state of the subject's language center.

[0049] In the control device 30 according to this embodiment, when the determination unit 32 determines that the sleep level is a second level different from the first level, the playback control unit 33 plays back the second content different from the first content. With this configuration, auditory stimulation can be provided to the subject with a variety of content depending on the subject's sleep state.

[0050] In the control device 30 according to this embodiment, the second level is at least one of stage 1 and stage 2 of non-REM sleep. In this configuration, when the subject is in a relatively light state of non-REM sleep, an auditory stimulus can be provided to the subject.

[0051] The technical scope of the present invention is not limited to the above-described embodiments, and appropriate modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiments, Level 1 (a state in REM sleep) is used as an example of the first level of sleep, but this is not limiting. Note that the first level may be, for example, in addition to or instead of Level 1, a level corresponding to Stage 1 or Stage 2 of non-REM sleep in which the subject is sleeping, i.e., Level 2 or Level 3.

[0052] <Variation 1> Furthermore, when the determination unit 32 determines the activity state of a predetermined region of the subject's brain, the threshold for the oxyhemoglobin concentration may be changed depending on the sleep level. For example, when the sleep level corresponding to the first level is high (wakefulness is low), the threshold for the oxyhemoglobin concentration can be increased, and when the sleep level corresponding to the first level is low (wakefulness is high), the threshold for the oxyhemoglobin concentration can be decreased. In this way, auditory stimuli can be applied to the subject more easily when the wakefulness level is high and more carefully when the wakefulness level is low, thereby reducing the impact on the subject's health.

[0053] <Variation 2> Although the determination unit 32 can determine whether the state is adaptive or non-adaptive based on whether the oxyhemoglobin concentrations in both the Wernicke's area and the Broca's area are equal to or greater than a predetermined value, the determination unit 32 may use the difference between the oxyhemoglobin concentrations in the Wernicke's area and the Broca's area instead of the oxyhemoglobin concentrations in the Wernicke's area and the Broca's area. That is, the determination unit 32 determines the state as adaptive when the difference between the oxyhemoglobin concentrations in both the Wernicke's area and the Broca's area is equal to or greater than a predetermined value (thresholds B1 and B2, respectively), and determines the state as non-adaptive when the difference between the oxyhemoglobin concentrations in at least one of the Wernicke's area and the Broca's area is less than the thresholds B1 and B2, respectively. In this way, when the oxygenated hemoglobin concentration and the deoxygenated hemoglobin concentration are both high, providing the auditory stimulus to the subject effectively reduces the impact on the subject's health without forcing the subject to further supply oxygenated hemoglobin. Furthermore, using the difference between the oxygenated hemoglobin concentration and the deoxygenated hemoglobin concentration allows for a relative value, making it easier to tolerate individual differences.

[0054] <Variation 3> Furthermore, when the determination unit 32 determines that the sleep level is a second level different from the first level, the playback control unit 33 can cause the playback device 40 to play the second content as content when a predetermined time has elapsed since the start of sleep. By doing so, auditory stimulation is provided to the subject close to the wake-up time, which can reduce the impact on the subject's health and increase the likelihood that the subject will remember the content after waking up. Furthermore, by using the second content as an advertisement, it can be effectively advertised to the subject. Alternatively, the second content can be set to a predetermined time before the subject wakes up, rather than a predetermined time after the start of sleep. In this case, it can also be linked to an alarm clock or the like.

[0055] It should be noted that each of the above modifications can be combined with other modifications. [Explanation of symbols]

[0056] C1...first content, C2...second content, L...period, t1, t2, t3, t4, t5, t6...time, 10...detection device, 11...head-mounted unit, 12...optical fiber channel, 12a, 12b...optical fiber, 13...information generation unit, 20...setting device, 30...control device, 31...acquisition unit, 32...determination unit, 33...playback control unit, 34...storage unit, 40...playback device, 100...memory fixation device

Claims

1. an acquisition unit that acquires brain activity information that is calculated from the oxyhemoglobin concentration or deoxyhemoglobin concentration in the Wernicke's area and the Broca's area of ​​the brain of the subject, and indicates the activity state of the Wernicke's area and the Broca's area of ​​the brain of the subject; a determination unit that determines a sleep level indicating the depth of sleep of the subject and determines an activity state of a predetermined part of the brain of the subject based on the acquired brain activity information; a playback control unit that causes a playback device to play content that stimulates the auditory sense of the subject according to the determination result of the determination unit; Equipped with The reproduction control unit reproduces a first content including details to be memorized by the subject as the content when the determination unit determines that the sleep level is a first level and that the activity state is a predetermined state. Memory consolidation control device.

2. the first level corresponds to REM sleep; The predetermined state is a state in which the oxygenated hemoglobin concentration in the Wernicke's area and Broca's area of ​​the brain is equal to or higher than a predetermined value. The memory fixing control device according to claim 1 .

3. When the determination unit determines that the sleep level is a second level different from the first level, the reproduction control unit reproduces, as the content, a second content different from the first content.

3. The memory fixing control device according to claim 2.

4. The second level corresponds to stage 1 or stage 2 of non-REM sleep. The memory fixing control device according to claim 3 .

5. an acquiring step of acquiring brain activity information calculated from the oxyhemoglobin concentration or deoxyhemoglobin concentration in the Wernicke's area and the Broca's area of ​​the brain of the subject, the brain activity information indicating the activity state of the Wernicke's area and the Broca's area of ​​the brain of the subject; a determination step of determining a sleep level indicating the depth of sleep of the subject, and determining an activity state of a predetermined part of the brain of the subject based on the acquired brain activity information; a playback control step of causing a playback device to play content that stimulates the auditory sense of the subject according to the determination result; Including, The reproduction control step reproduces a first content including details to be memorized by the subject as the content when the determination unit determines that the sleep level is a first level and that the activity state is a predetermined state. Memory consolidation method.

Images